Indoor Camping in Fortiﬁed Heritage Buildings: A New Way of Sustainable Tourism Valorization

: Indoor camping is an innovative, sustainable model of accommodation, the least intrusive one in solid facilities. Its temporary tourism function demands almost no additional construction work, meaning no permanent modiﬁcation of space is needed for tourism purposes. Fortiﬁcations and defence buildings are recognised as valuable cultural attractions and present an anthropogenic resource with potential for touristic valorisation, both as sightseeing facilities as well as accommodation facilities. This paper explores the connection between the requirements of heritage protection of fortiﬁcations and the requirements of the application of indoor camping in these fortiﬁcations. The purpose of this paper is to help conserve fortiﬁcations by providing funding for their maintenance with the application of this innovative accommodation model respecting the principles of sustainability and health and safety standards in post-Covid tourism. The goal is to provide a general framework that could reconcile tourism businesses on one side and conservators on the other. The main scientiﬁc contribution is summarised in the framework of adequate implementation of indoor camping in fortiﬁed buildings according to conservators’ requirements. The interview technique was used to assess this. The authors found that indoor camping can be a suitable accommodation model in fortiﬁed buildings. The key limitation of the model is based on the fact that an individual approach is necessary for every heritage building, as well as fortiﬁcation, since they are unique. Therefore, each application of an indoor camping model should receive a proper conservators’ permit before the entrepreneurship venture. Furthermore, the opinions of key stakeholders were also investigated.


Introduction
The indoor camping model idea came to life in another context: the problem of seasonality of tourism, which has long been addressed with the intent to flatten peak periods and redistribute more evenly the number of tourists [1]. This paper, in addition to addressing the current issue of accommodating tourists in cases where destination's capacity is insufficient [2], by applying this model to heritage buildings in order to maintain them, seeks to be the solution to two issues affecting tourism sustainability, as many heritage buildings strive for renovation, maintenance and valorisation. In the paper the authors are researching if the proposed solution to such situations-the indoor camping model-could also be implemented in vacant heritage buildings, located at attractive buildings which do not have touristic categorisation. Considering the predominant segment of potential users of indoor camping in heritage structures, the authors emphasize the educational value of the innovative concept. Learning about heritage contributes to its responsible and sustainable valorisation and helps to avoid the danger of saturation and destruction due to over tourism. The Covid-19 effect on the travel and tourism sector is disruptive, implying the concept of indoor camping accommodation model should be adjusted to the new requirements of safety and health standards which is not stressed in this paper. Therefore, the main hypothesis states: indoor camping can be implemented in fortified heritage buildings without affecting their integrity by adhering to the principles of conservation and sustainability. In order to discover the possibilities and the legal framework of implementation, the authors researched the topic by conducting structural interviews with experts and relevant tourist destination stakeholders that could enable interested stakeholders to implement indoor camping as a new form of accommodation.
The key research questions arise from the main hypothesis and thus investigate: The main focus of the paper is to research the application of the indoor camping model to historical buildings, i.e., fortified cultural heritage that could provide accommodation space and services within the sustainability concept. In order to answer the research questions regarding the feasibility of application, an interview with the first expert, a conservator, was carried out.
The interview with Mrs. Nevenka Šuran Marinčić, architect and conservator counsellor for tangible cultural goods within the Ministry of Culture of the Republic of Croatia-Directorate for the Protection of Cultural Heritage, Conservator Department in Pula, was conducted on 22 January 2018 in the Conservator Department in Pula. The semi-structured interview lasted three quarters of an hour. The goal of the interview was to confirm the main hypothesis that indoor camping is suitable for implementation even in protected heritage buildings with the focus on fortresses. The author annotated the answers in the form of notes. The written interview was sent to interviewed conservator for pre-approval and revised on 24 January 2018.
During the interview, the conservator provided the researcher with a "Conservator study" of the fortification Monte Grosso, Pula, to better understand their modus operandi. Therefore, in addition to collecting primary data, in order to achieve the stated research goals, secondary data were also combined. According to the answers of the conservator, since the application of the indoor camping model depends on urban permits which define the purpose of land use, also the representatives of the local government of the municipality of Svetvinčenat, Croatia, interested in the implementation, were interviewed, along with those of several stakeholders. The opinions of stakeholders were collected on more occasions during autumn of 2020. There were two meetings, one with representative of local authorities (2) and the other with the representative of local community (4) and representatives of private sector (6). In total, 12 persons agreed to answer to authors' questions. Among the representatives of private sector there were four representatives of private accommodation (there are eight private accommodation facilities in the centre of Svetvinčenat). Data from the stakeholders where collected in the form of a semi-structured interview. In the timespan of 30 min the interview's respondents where firstly introduced with the indoor camping model and the possibilities of application. Every respondent was asked to list positive and then negative aspects of possible application of the model from their point of view. They explained all the given answers guided by sub-questions.
The limitations of the selected method steam from the subjectivity of respondents thus present ambiguities, inherent to human language. The local focus can be deemed as a limitation, however, all the interviews can be easily replicated.
The results of these researches are summarised in a matrix serving as a guideline of application of this model bearing in mind the special features of fortified heritage (Table 1,  Table 2) and a table listing pro and cons of relevant stakeholders (Table 3). Table 1. Interview core question referring possibilities of organisation of indoor camping model in fortresses heritage buildings.

Researcher:
Conservator: Who is doing the assessment and writing the Conservator elaborate?
Qualified experts certified by the Ministry of Culture.
There is a list of authorised experts.
What about infrastructure installation in a fortification?
It depends on the size of the intervention. If it were about drilling a small hole, it would be possible; however, destroying a part of the wall is unacceptable. It is necessary to check the technical accuracy in case of existing infrastructural connections. New installations inside and outside the building should be aligned with conservator requirements.
Who should suggest and approve the installation of electricity?
It should be defined in the project of electric installations as part of the project documentation for that intervention.
What is the attitude of conservators towards investments?
Practice has shown that monuments assigned to users manage to survive. The use of a monument must correspond to the significance of the monument. In this respect, in order to maintain, preserve and revitalise them, every use of cultural goods in harmony with conservation guidelines is useful and desirable.
Source: Authors' contribution.  The third research refers to the survey of graduated students of the Faculty of Economics and Tourism "Dr. M. Mirković", Juraj Dobrila University of Pula (Croatia), whereas the key research instrument was an originally developed questionnaire. The research, conducted only online from 7 January 2021-11 January 2021, aimed at discovering the perceptions of young generations about staying in such an accommodation based in a heritage building. The total number of respondents who completed the questionnaire was 102. All the questionnaires were valid.
Besides being an interesting topic for the academia, it could be of interest to experts in tourism and heritage management, public sector (conservators, tourism and similar ministries), local government and entrepreneurs.
This paper is composed of four main chapters. The introduction to the topic and including elaborated methodology include the research design and methodology explanation; it also presents why this qualitative method of research is chosen and ensure the value of obtained and summarised results which are presented. The second chapter, Materials and theory is diversified in subchapters where theoretical review and the model of indoor camping are presented. It includes elaboration of problem context: sustainability, culture and the protection of fortified heritage together with conducted interview in chapter three. These results are explored in relation to indoor camping requirements which were detected and set out as an innovative pioneer temporary accommodation structure. After discussion the authors present conclusive remarks and present recommendations for future actions and possible development of the pilot project and field research in chapter four.

Fortified Heritage Used for Tourism
The concept of cultural heritage is broad and complex. There are many definitions of culture, heritage and cultural heritage [3] of tourists-motivated and inspired by culture [4][5][6]. Well known are the principles of UNESCO, the umbrella institution for management and preservation of the world cultural heritage [7] which point out the importance of sustainable preservation of built heritage. Moreover, the importance is emphasised of those tourists whose primary motive for arrival is not touring heritage sites but, by visiting them and staying there, acquainting themselves with them and learning about the local heritage; immersed in authenticity, they develop deeper understanding and appreciation. Park [8] presents fundamental guidelines and core heritage tourism, studies marketing evaluation potentials and gives answers to a series of questions, from sustainability and carrying capacity to sociological aspects associated to education, identity and urban and rural regeneration which heritage tourism enables [9].
Cultural heritage is made up of movable and immovable cultural property of artistic, historical, paleontological, archaeological, anthropological and scientific significance. Archaeological sites and archaeological zones, landscapes and their parts, which witness human presence on the premises of those purposefully constructed structures, attest to the historical culture of living and working and represent valorisation resources [7]. Cultural heritage values are recognised as aged, historical, cultural, artistic and authentic, as defined by the Ministry of Culture of the Republic of Croatia [10]. Moreover, cultural heritage is studied as a basis for the development of new products and authors [11][12][13] explore the possibilities of using cultural heritage for destination tourism development. Bujdoso [14] present intricately the context of "heritagization" as a platform for the development of sensation, i.e., experiences of innovative cultural tourism.
ICOMOS (International Council on Monuments and Sites [15] defines heritage as a broad concept which includes natural and cultural environments. It notes and expresses a long process of historical development, forming the essence of various national, regional, native and local identities and is an integral part of modern life. It is a dynamic reference point and a positive instrument for growth and change and economic valorisation, stresses [16] while Chong [17] point to the importance of synergic action of all destination stakeholders in that valorisation. The strategies proposed include stakeholder collaboration and involvement, stakeholder empowerment and the adaptive reuse approach. The specific heritage and collective memory of each locality or community are irreplaceable and important for the development, both now and in future, declares [18]. Authors [19][20][21] discuss the importance of protection and preservation under the concept of sustainability, while Dans [22] analyse socio-cultural aspects and social values of heritage sites. Furthermore, Urošević [23] explore sustainable use models and strategies and recognise sustainable development of cultural heritage as a driving force behind community revitalisation and new development. Jamieson [24] study urban cultural heritage and aspects of carrying capacities, stressing the negative impacts and possible damage which excessive exploitation may cause. This also includes physical changes to buildings, extensions and unprofessional adaptations which irreversibly alter their authenticity; every intervention on such buildings, therefore, must be in line with the instructions provided by cultural heritage conservationists, experts who take into consideration the structure, its characteristics and values in the context of the period from which it originates, materials of which it was built and equipped, colours, its surrounding area and other factors which affect its originality [25]. Authors [26] deal extensively with the policy of management and conservation and consider its different aspects. Further to this, Williams [27] examines the meaning and effectiveness of world heritage designation, while Forrest [28] studies and analyses cultural material and non-material heritage through the legal and institutional context.

Fortification Heritage Buildings
There are many similar definitions of tourism resources, where the main point lies in assessing their tourism potential i.e., "the concept of tourism resources includes those natural or social resources which can be valorised through tourism, namely those phenomena, structures, events, etc. which temporary visitors (tourists and day visitors) visit in the course of their travel due to their high degree of attractiveness" [29].
Material cultural heritage can be classified into different categories. Movable heritage includes paintings, sculptures, church furniture, treasures, arts and crafts products, ethnographic, archive or library materials, while immovable heritage includes monuments and structures (archaeological sites, monumental entities, memorial sites and structures, individual sacral structures, individual secular buildings and structures and garden architecture) [9]. In consideration of the topic and the valorisation potentials, the problem area of fortification facilities, as immovable material heritage, is presented; a tourism resource which is important for valorisation and inclusion in the tourism economics, either as an infrastructural accommodation facility or as a tourist attraction [30].
Throughout history, geopolitical and strategic situations of some areas required the construction of fortification systems whose role was, both during wars and peace periods, very important. Fortification structures often played an important, sometimes decisive role in exiting or concluding wars; with their appearance and armament they prevented invasion of enemies in the direction where they were situated, and ancillary structures had different functions within the system support, from maritime forts, studied by [31] and [32] to inland fortification systems [33]. War affected areas, as well as the structures associated with them, are almost always places of reverence, so their valorisation should be approached with special care. Uzell and Ballantyne [34] define "heritage that hurts", while Beech [35] further claim that with the passage of time, instruments of war could become tourist attractions. The exceptional character of the architecture, blending into its surroundings [36] and the historical context, supported by storytelling, positions fortified structures on the map of destination attractions, while complying with the required safety and technical standards and accessibility.
Moreover, there is the issue of fortified facilities (strongholds, shelters, bunkers, military barracks, fuel tanks), related to their inadequate use, i.e., they have been abandoned, left to decay, devastation and theft. On occasions, the local population also contributes to such a situation due to insufficient awareness of their historical significance and lack of financial funds needed for their preservation, valorisation and promotion. Therefore, the importance of raising awareness and creating educational programs both in the local community and among tourists who would stay in heritage buildings is emphasized [37] Through workshops and lectures led by experts that would be organised for the purpose of heritage presentation, the intangible context of values would be valorised. [38] The storytelling would contribute to sustainable evaluation and respect for authentic history and tradition [39]. Given the availability and power of digital technologies, various forms of heritage presentation are offered in order to educate and raise awareness of values, from multimedia content and presentations, applications on social networks, gameplay to personal guides and educational workshops. In valorisation of fortified construction heritage, the importance of traffic access and construction of roads in the vicinity of such structures are considered in order for the areas with less developed tourism to also be economically empowered by a financial inflow of tourist activities, thus simultaneously preserving the buildings which have reached a high degree of degradation, becoming both a visual and general burden on the environment where they are located.

Fortification Heritage in South Istria Region-Initiatives for Valorisation
Istria is one of the most developed tourism regions of Croatia. Its biggest town is Pula, the richest one in term of fortified heritage, boosting many well-preserved Austro-Hungarian fortifications and around 80 other military solid, historic facilities. It is possible to valorise Austro-Hungarian fortification heritage through different projects, directed to cultural heritage and to affirm it by means of education, tourism and numerous interdisciplinary activities and programmes. They can be realised through the public sector, public-private partnerships and different modalities of institutional support and assistance. It is manifested through investment in infrastructure, superstructure, education, provision of information and establishment of lasting values through foundations, museum displays and exhibitions [40].
Viewed within the context of evaluation of the Pula fortification heritage, there is potential for the creation of a unique exhibition about the fortification ring from the Austro-Hungarian period, by which the entire history of the Pula fortifications would be consolidated, and the local population and tourists made aware of the problems of these fortifications. One such project-"Fortification Museum-Pula" was realised with the support of the National Tourism Board in 2009, which, through a modern design and multimedia approach, linked the historical context and modern trends of valorisation of culture and, with an organised depot of archival materials, constitutes a platform for the creation of the museum of the Pula fortification ring. Furthermore, through exhibitions, seminars and adventure tourism, the Zero Strasse project valorises the underground corridor, built in the Austro-Hungarian era, situated not far from the Twin Door in the centre of Pula and open to the public. The corridor is some 400 m long, has a central hall and corridors are between three and six metres wide and around 2.5 m high. The Pula underground corridors are made up of a forty or so kilometre-long underground network which connects Pula fortifications. Such an exceptional location can constitute a framework for new activities and tourism offer in the Pula fortification network [41]. In consideration of valorisation potential of the South Istria fortification heritage, the problem area of unresolved property ownership and legal relationships is analysed; the majority of the facilities are the property of the Ministry of Defence of the Republic of Croatia or the state and only five of them are owned by the town. As resolving property ownership is a prerequisite of a successful investment, it is essential that it should be ensured.
In addition, valorisation of fortifications in South Istria has been carried out by the Adrifort project (Adriatic Fortresses and Military Areas), in which twelve partners from Italy, Slovenia, Croatia, Montenegro, Albania and Greece took part and where each region valorised its fortified military heritage [42]. Through infrastructural and material investment, as well as through intellectual and organisational support, six facilities in the Pula region, dating from the period of the Austro-Hungarian Empire, were encompassed by the Adrifort project, namely the coastal polygonal armoured fortress of Punta Christo, coastal horseshoe fortress Monte Grosso, with adjoin artillery battery, artillery battery Valmaggiore, round fortress Munide, coastal artillery battery Zonchi and St. Michael's Fortress. The Pula fortification system was being built mainly during the second half of the 19th century and completed in the course of World War One for protection of the central war harbour of the Austro-Hungarian war navy. The system comprised 26 forts, 8 artillery batteries and some 60 batteries which were, to a significant degree, interconnected by trenches and underground tunnels. Three defence fortification rings around the town of Pula have been conceived and constructed, two in the area of the town itself and one, which spreads throughout the town surrounding area. The external ring of Pula fortifications, in which also five of the fortresses, included in the Adrifort project, are situated, covered the surface area of forty thousand hectares and, through the project, the most is invested in the Punta Christo fortress.

Indoor Camping: A Sustainable Accommodation Model
Indoor camping is a theoretical model of accommodation aimed at providing accommodation in peak periods of demand by putting in use for tourism various buildings whose primary purpose is not accommodation. It is an innovative model that is developed according to the researched preferences and demand of youth tourists' segment [1]. The pilot application in tourism destination based on scientific exploration of complex aspects and conservator's requirements is proposed. Indoor campers sleep on the floor, in their own sleeping bags or those provided by the establishment. The latter blurs even more the borders between camping and stays in solid accommodation facilities, as camping implies the use of one's own equipment. It is a hybrid model combining the shelter provided by buildings versus camping in a tent (indoor camping thus requires no tents) and the neighbourhood atmosphere of camping, without any walls dividing camping places. Taking in account the new normal and social distancing because of COVID 19 virus, it is recommended that one room is shared only by a group of guests who travel together. Housekeeping services must be provided, while the reception might be available on demand. F&B are not mandatory. It is therefore a simple, no frills, model suitable mainly for a young target market and an excellent accommodation alternative in case of densely visited events where walking distance to the locations is a plus [2].
The minimal requirements of indoor camping are [43]: housekeeping services, -front office services on demand, -minimally 12sqm per indoor camping place (for three persons) and + 3sqm per every additional person. Accommodation units have to be adequately marked as well as the passages among them, -at least one electricity outlet per person for each indoor camping place, a minimal number of sanitary facilities (one basin, shower and toilet for each 15 persons of each gender). It would be ideal having more toilet amenities, at least one per room.
Youth segment is identified as predominant consumer segment of indoor camping accommodation product. Examining potentials of development and by analyzing youth tourism preferences, the necessity for organization of accommodation facilities compatible with their needs and financial solvency is identified. The youth tourism trends point to the fact that young people, as a part of the Y and Z-Millennials generations [44] are looking for low budget accommodation with all safety and hygienic prerequisites and catering services, and all of that in the vicinity of the event venues. Given the dispersion of accommodation and catering facilities, this represents a limiting factor, as event venues can hardly meet the quantity of demand for adequate accommodation facilities. Solutions are proposed in traditional organized hostels, privately owned accommodation facilities and campsites, which represent organized permanent accommodation model, as well as in the innovative model of temporarily organized facilities, indoor camping.
This model, because of its characteristic, could be especially interesting to youth Deeper understanding of the indoor camping demand requirements is gained through the research conducted in 2016 where Benckendorff et al. [45] explored attitudes of 139 Croatian students of Juraj Dobrila University of Pula and 15 ERASMUS students coming from Spain, France, Poland and Czech Republic. In Croatian sample was 89.9% of undergraduate students and 10.1% graduated students, while in Erasmus group 53.3% of undergraduate students and 46.7% graduated students. Looking together 85.1% are undergraduate students and 14.3% graduate and sample counted 35% of male and 64% of female participants. The survey questions explored (1) where youth consumers usually stay during travelling, (2) way of travelling, (3) usual type of accommodation used by youth and (4) set of questions about proposed indoor camping model and its features.
The research showed that students mostly stays in private apartments/accommodation (47%), followed by hotels, resorts (24%), hostels (21%), on the last place are camping sites (42%) 87% of students did not use couchsurfing and did not travel as backpackers but they would try it, if they got the chance (56%). Students agree that indoor camping is a welcome accommodation model in a time of great events that they would use (44%), they agree with the size of the indoor camping accommodation unit, that is 12 m 2 for 3 people and for each additional person 4 m 2 , that is sufficient for bed (39%). They consider important (agree) having wi-fi (51%), safe (31%), shared kitchen (53%), gathering room (40%). Most of them would use this type of accommodation for only 1 night (47%), 2-4 nights (45%) and more than 4 days only 0.07%. What is encouraging is that 58% students think that this type of accommodation provides new experience for tourism. Thus, this model is acceptable for youth during big events and it should be expanded by adding common/shared kitchen and wi-fi connection. Safety is very important for the surveyed population so adding a safe deposit box for them is not enough, some also recommend to hire a security. This model is suitable for students and young populations. Its sustainability its enhanced by its temporariness that is in accordance with the collected answers.
The particularity of the model is the temporality of the business: any building which is transformed into an indoor camping facility can be easily restored to its original function. This is an advantage over other sustainable models that also use existing buildings, but which have been permanently modified for tourism purposes [2]. Indoor camping is intended to be an asynchronous model cessing temporary the primary function of the building or might function as an add on to the primary function of a building, however operating also only short term. Namely, in case of operating (part of) the building on the long run, not only seasonally, it makes sense to arrange it as a solid accommodation model such as a room, apartment, hostel etc. The possibilities of implementation of this accommodation model are various, however the most convenient solutions i.e., buildings which could be easily converted to an indoor camping are those which already have built-in toilets with showers and empty surfaces e.g., gyms, wellness centres, ballrooms, airports etc. [3].
Moreover, the funds generated by this unique possibility of sleeping in any heritage building-providing tourists an experience melted with educational, socio-cultural and eco-friendly components-are reinvested to preserve the building itself, which is another remarkable aspect of the sustainability of the model.

Fortification Heritage-Possibilities of Implementation of Indoor Camping Model
The restoration of cultural and historical monuments and heritage often included their use for cultural and art purposes. Monuments have been restored throughout the recent times and museum and gallery facilities have been formed in them, as well as the other cultural institutions, focused mainly on short-term visits. Heritage buildings, which preceded the industrial revolution, including churches, castles and medieval fortresses, had in general the priority of valorisation. With a dynamical development of the society, modern trends, however, point to the valorisation of curiosity of human building skills from the modern times (since the development of industry, technology and transport) in accommodation capacities for the purposes of intensification of experiences in relation to the experience gained by a short visit to such structures. It is important to mention that fortresses are especially suited for accommodation of tourists due to their unchangeable fresh temperature, without investment in air conditioning and the uniqueness of the ambience presumes deprivation of various technical prerequisites which some other modern accommodation facility models should provide. On the other side, some authors [46] point out that when the reuse of heritage buildings is planned, the firm legislative regulation with standards and requirements should be set because of the danger of negative impact of non-regulated hospitality operations on sociocultural authenticity.
Many forgotten and neglected structures, rejected due to the development of new technologies and abandoned due to new demographic concentrations in certain areas can again be transformed into profitable facilities which will, apart from producing financial income themselves, also activate other economic results. Authors Fedorczak-Cisak, Kowalska-Koczwara and Pachla [47] explore different criteria related to the selection of a new function of heritage structures and point out the multidimensionality of the problem. Inductively, new additional facilities are created and initiated in the surrounding area and in the vicinity of converted attractions (structures). This leads to the development of new destination offer which networks and coordinates stakeholders' activities and contributes to the competitiveness of the destination itself.
The reuse of churches and spiritual buildings and potentials along with cases of their transformation into sustainable tourism accommodation structure are also explored [48,49].
For safety reasons, in the course of their history, almost every country built military infrastructure for defence of their country, which was mainly constructed to resist as much war devastation as possible, namely, solid structures, and this is why the majority of historical bunkers and forts still today have rather stable or completely stable building statics. Among them, in Croatia, we can distinguish the examples of the already mentioned Pula fortification ring, the Brijuni Archipelago fortifications, fortresses-castles, the fortified city of Dubrovnik, the Senj tower and other structures, constructed for the purposes of military defence [50]. Apart from this, the size of these structures is of sufficiently generous dimensions and it is interesting for conversion for the purposes of tourist accommodation.
It is not uncommon to consider such structures as a potential investment due to their attractive massive appearance. What makes it interesting is the unique location as such fortifications or bunkers are usually located in the middle of the sea, on cliffs, embedded in rocks or caves etc. An international example of such fortress which has today become a hotel is the Spitbank fort in UK. Another example refers to the Project Mamula / Orascom related with valorisation of fortification in Boka Kotarska in Montenegro, which is in the phase of procurement of planning permissions [51]. San Martino Castle (Italy) which now days is in use as a hotel, it is a good example of heritage restauration in accordance with sustainability principle of saving energy, based on innovation in different fields [52]. As large number of heritage buildings are located in rural isolated locations, very often in nature without electricity power that is identified as important problem of adequate and sustainable use. The solution could be found through implementation of Integrated Solar Thermal (BIST) panels integrated into the building envelope, combining the energy generation with other functions, such as noise, weather protection, thermal insulation, sun shadow, and other aspects. Nowadays, the dynamism of the market allows to design highly compatible products which look like traditional architecture materials. This situation fosters the integration of these products in the BIPV and BIST systems within the heritage sites, especially thanks to the use of advanced customization processes, special and lowreflecting glasses, and innovative cost-competitive coatings, continue [52].
Indoor camping model in heritage buildings has to be implemented in accordance with conservators and therefor the right eco-efficient energy supplies such as BIST should be implemented in its sustainable operational use concept as well as the application of sustainable eco efficiency (energy, water, waste) technologies in heritage structures without impacting their heritage value. All indoor camping requirements can be fulfilled based on sustainable and non-destructive principles of construction. The Figure 1 below shows the indoor camping model in heritage buildings, which is the usual one, enlarged by conservators' permit. The revitalisation of heritage buildings should provide financial and cultural benefits to the local community and, in accordance with this, indoor camping could offer a good sustainable model that reconciles business and heritage. As the economic returns of heritage buildings and sites are a key aspect for the sustainable tourism the valorisation should be done responsibly with the benefit of both, local community and private capital in consideration. The business models should be adjusted to the ownership circumstances because heritage buildings can be in different ownership from public to private which will define the implementation model [53]. Independently of its ownership, indoor camping model in heritage buildings has positive and some negative aspects, as perceived by stakeholders (Table 2), although its multiplicative effect is unquestionable. This innovative model affects local entrepreneurs by increasing the number of tourist arrivals in the destination, especially when targeting guests with higher purchasing power. Bars, shops and restaurants, can have direct benefits, as these services are not provided within the basic indoor camping model.
With the growth of cultural tourism in the last years, this specific implementation of indoor camping in fortified heritage buildings is a feasible entrepreneurship venture.

Interview with Conservator
The interview started with a short introduction about the goals of the research: the possibility of application of an innovative accommodation model in heritage buildings. The first question, related to the set of rules conservators have to take into account in order to protect heritage buildings, was a stumbling stone. Instead of an answer, there was a counter question regarding which specific fortification (building, monument) we had in mind. The authors were interested in heritage facilities (buildings) in general, in order to test the stated hypothesis.
The The researcher reframed the question in order to check for specific protection guidelines. Basic guidelines are set in the Protection act (a document used to list a certain good in the Register of cultural heritage). Within the above stated framework, conservators have an individualised approach matching each protected heritage building. Conservator stated that heritage buildings can be revitalised according to various functions (e.g., tourism, social); however, the realisation depends also on urban plans upon which heritage buildings are based. Conservators' protection of heritage buildings involves a comprehensive approach. It focuses not only on architectural preservation, but also on the surroundings (e.g., in treatment of fortified heritage the corresponding area of the fortification is significant, including its greenbelt).
Upon completion of the conservation procedure, a permit for interventions on cultural goods is issued. The conservator process is complex and involves the production of several types of elaborates. For the sake of brevity, only the most important documentation will be mentioned (exploration of the historical development of the building or site, detailed documentation of the existing state of the building, project of renovation). Conservators' permits are based primarily on the compatibility with Specific conservator requirements and Conservator studies. A Conservator study is a detailed research document whose main aim is to define professional guidelines for designing project documentation of a complete reconstruction of the facility. Accurate interpretation and analysis of a protected facility includes the understanding and interpretation of its architectural, urban and historical context. The implementation of the conservator process usually implies their supervision during construction works and on completion, explained conservator. The resumed results of interview are presented in discussion section (Table 2) and the research core questions authors present in complete ( Table 1). The indoor camping model was then presented and concrete questions about the required works were explained: the signalisation on the floor, bathrooms (which could also be mobile and set inside or outside of the building), electricity inside to illuminate camping places, passages and providing power outlets and safe deposit box wardrobes. The answers to those issues are presented in Table 2 in the next chapter.
The attitude of the conservators was favourable towards such a non-invasive model of accommodation in heritage buildings. It was concluded that the goal of indoor camping as a sustainable and temporary hospitality model and conservator requirements were aligned. Concerns were raised in the discussion regarding the economic sustainability of such investments, given the temporary character of the business.

Exploration of Demand-Youth Segment Attitudes
In order to achieve better understanding of youth demand preferences regarding sustainability and heritage perception as a continuance and expansion of previous studies, the research of youth consumers' attitudes is conducted. The survey which was conducted among 102 graduated students of Faculty of economics and tourism "Dr. Mijo Mirković" (Juraj Dobrila University of Pula) from January, 7 until 11 January 2021 analysed the perception of youth regarding indoor camping in heritage buildings. The age of students is 21-23, whereas there were more female than male respondents (65% female).
Likert was used in questions that follow. Survey showed that for 37.3% respondents reinvesting money in heritage preservation is important and strongly agree with the claim, while 25.5% agree and 28.4% are neutral. Around 9% of students do not see preservation important (not agree and strongly do not agree). The reasons for choosing indoor camping as accommodation model are also questioned in the survey. The respondents graduated the reasons according the Likert scale. The first mentioned reason was sustainability with which agree 34.3% of respondents and strongly agree 22.55% of them. Most of the respondents answered that price is important for them, so 39.21% agree and strongly agree 18.62%. New experience and adventure is the reason with which strongly agree 56.86%, more than half of students, while 28.43% agree with it. 39.21% of respondents, most in the category, agree that location of indoor camping near the event is important as reason. On the other hand, 25.49% strongly agree with the claim. 49.02% of students strongly agree that unique location of accommodation situated in heritage sites is important as reason, while 26.47% agree. Moreover, with the claim of the importance of cultural and historical value of the building most agree (35.29%), and strongly agree (21.57%). With the possibility to socialize with the youth of similar interest strongly agree 38.23% and agree 34.31%. In the all answers the majority of the answers where in the second half of the scale (agree and strongly agree), while strongly disagree, disagree and neutral where answered in minority.

Pilot Case Preparation: Svetvinčenat Castle and Indoor Camping
The mentioned model is possible to apply in the location of Svetvinčenat, which is situated in the Municipality of Svetvinčenat in Istrian region. Today, the municipality has 2000 inhabitants, while in the town of Savičentat live 200 inhabitants. Svetvinčenat, Savičenta, San Vincenti, are the three names for the same place. The name derives from the name of its patron, Hispanic martyr Saint Vincent and the abbey holding the same name around which the municipality has developed.
In the recent years, Svetvinčenat has become an Istrian tourist hot spot due to many events taking place in the attractive historical corners of this renaissance town. It has a very interesting history, which can be seen in historical sites, such as its main square ("Placa"), Morosini-Grimani castle, which is the landmark of the village and one of the most important Venetian fortifications in Istria. Due to this castle, Svetvinčenat also developed a Medieval festival, which attracts many visitors [55].
The stone castle Grimani, the best preserved castle in the peninsula of Istria and the largest Svetvinčenat building, used to be the destination for tradesmen, soldiers, aristocracy guests and travel writers. Its first fortress was built in the early 13th century, but the turbulent war's years resulted in its frequent destruction, which required the reconstruction and changes to the castle's appearance. Its owners were bishops and the families Castropola and Morosini. After them, the ownership of the castle was gained by the Grimani from San Luca, a Venetian family. The castle took its present appearance in 1589 when Marino Grimani renovated the burnt castle according to designs made by the Venetian architects Scamozzi and Campagne.
On its three corners there are three towers, and the fourth is the palace for gentlemen and a flat for the captain. The towers were used to control the entrances to the town and were in the past, as today, connected by fortress walls which also have a supporting wall at the bottom and, from the inside, there is a balcony throughout its length, from which the guards observed through sight-holes. On the gate, apart from the drawbridge, there was also a big descending barrier. Above the entrance, there is the castle's coat of arms, which is the present coat of arms of Svetvinčenat and coat of arms of the Grimani di San Luca family. Beside the large yard, inside the castle, there were situated an apartment for the town steward, a warehouse for payments in kind and ammunition, rooms for 200 musketeers and lancers and a very safe prison-under the ground. In the 19th century, the Grimani family gave the castle over to bishops who gave it to the municipality earlier this century. During World War II the castle was burnt one more time.
Indoor camping in Morosini-Grimani Castle could be a great solution during the peak season and during the Medieval festival in Svetvinčenat. It could help all the participants to be situated in the same place, enjoy the unique atmosphere of an original castle and socialise with other medieval fans and similar associations' representatives. The same part of the castle could be used for two purposes, for the indoor camping and for the escape room concept, called Escape castle. Thus, the authors made a comparison of these two models, to see if they could coexist.
Escape Castle in Svetvinčenat did not implement the classical concept of the escape room; it does not have riddles only in one room. The concept uses most of the castle space: information point, dungeon, armoury, three towers and the throne. Every one of these castle spaces presents one riddle. The theme is medieval, so the sword in the stone represents the final stage of the game. The one who succeeds in pulling the sword out of the stone by solving all the riddles discovers the final puzzle, the stone inscription. This unique concept, not only in the County of Istarska, but also in the whole country, attracts many players during the year. The castle is open for visitors and players throughout the whole year. Players are not only tourists who visit Svetvinčenat during the summer, but also locals, who are attracted by this interesting concept or just love to play escape room games. Around 2500 people played the game in 2018, while around 3500 people visited the castle without playing it [56]. According to the State Bureau of Statistics [57] in 2017, the Municipality of Svetvinčenat had 13,047 arrivals, of which 303 were domestic, and 12,744 were foreign. As for overnights, it had a total of 122,092, of which 1221 were domestic and 120,871 were foreign. Newer data of visitors in 2020, are not yet listed.
These are significant numbers for small community, which are mostly achieved in the three summer months, June, July and August. As the Castle is also very attractive for different events, like weddings, business meetings and theme dinners, it is very important that the indoor camping is used only periodically or occasionally, especially during the Medieval Festival in August, when many visitors and participants come to Svetvinčenat. As stated by the Municipality company which manages the castle, around 10,000 visitors come to Svetvinčenat during the 3 days of the festival and approximately 200 participants are involved.
The implementation of the indoor camping model is possible in the square tower, which has four levels measuring approximately 10 m 2 each, of which two can be used, making a free implementation space of 20 m 2 . Sanitary facilities are dislocated and are situated in the other part of the castle; not far, but they could be supplemented with chemical ones.
The ideal business model would be a public-private partnership in which the Municipality, as the castle owner, would allow private subjects to implement indoor camping by providing sleeping bags or setting up automats with them. Housekeeping services and front office services should be something that could be outsourced to private subjects, but also could be in competence of the Municipality (its company which manages the Castle). Regarding the longer lasting concept of indoor camping, timing the activities and managing the implementation of the concept would be crucial for this business model. As indoor camping is a very flexible, adaptable and non-invasive model, implementing a longer lasting concept would not be easy, but it would be achievable.
The indoor camping model in the Morosini-Girmani Castle could also be used to complement the Medieval Nights, which are held during the summer or as a thematic addition to medieval dinners or any other event.
As seen from the above Figure 2, indoor camping could be situated in the square tower that spreads on the surface of just 20 m 2 . According to the requirements of the indoor camping model, maximum 5 persons could sleep in the tower. For some other occasions, for example, during festivals, in agreement with the Municipality, it is possible to sleep in other parts of the castle, which provides additional space and increases the number of persons who can sleep there.
Since the implementation must comply with the conservators' requirements, the authors provided an overview of the suitability of implementation of the model in fortresses in the discussion below.

Discussion: Implementation of Indoor Camping in Fortified Heritage-A Synthesis
Since the indoor camping model is not a recognised type of tourist accommodation, it can be applied in practise with a conjunct action by interested parties in a bottom-up approach. The feasibility of the model should include further steps: (1) identification of heritage building that could be valorised trough indoor camping through various criteria including: sustainable resources, cultural and educational context, activity and adventure, (2) identification of stakeholders responsible for managing a certain heritage building interested in running an indoor camping and exploration of their attitudes and needs, (3) relevant cultural and tourism authorities which could provide and assist with the legislative framework needed and associated permits along with (4) local government and their jurisdiction, as well as other interested stakeholders.
The appropriateness of the indoor camping model in heritage buildings is shown in Table 2.
The main issue related to the implementation of indoor camping in certain heritage buildings depends primarily on urban plans and their appointment in zones allowing tourism purposes.
The key requirements for the implementation of indoor camping in heritage buildings are infrastructure-electricity primarily, and water and possibly sewage. Infrastructure might be distributed according to the conservators' permit. Eco-efficiency measures are welcome, especially dealing with electricity provision like solar systems [58] and various types of smart sustainable energy efficiency solutions related with hospitality industry sector including sustainable resources management [59]. Mobile toilets and showers might be rented out. Additional amenities (facilities) are placed in visually neutral positions, in order not to compete with the historical building or its significant elements, paying attention to an adequate landscape integration. Marking passages and borders of indoor camping places can be accomplished without any permanent modification. Nevertheless, in practise, each heritage building's adequacy for the implementation of indoor camping should be individually studied in terms of conservators' requirements.
The above analysis shows that indoor camping is a model which can be implemented in heritage buildings, in cases where it is situated in tourism-purpose zones and other adequate urban zones (e.g., residential) and set in accordance with a conservators' permitwhich confirms the starting hypothesis. The temporality of the tourism business in protected heritage facilities is a specific characteristic of indoor camping [2] allowing the primary function of any building it is based in to be retained. The current legal framework does not recognise such a multifunctional use of buildings, as urban zones are strictly predefined, thus limiting the operability of indoor camping mainly to tourist zones. In addition, the authors listed the pros and cons of using the model in heritage buildings for implementation of indoor camping on occasions with larger numbers of people. The presented Table 3. summarises the opinions of interviewed stakeholders.
Analysing the table above it is possible to sum up that every stakeholder has some kind of interest in indoor camping implementation. Implementing the model would also boost entrepreneurship in the local government. Bars, restaurants and shops, but also local agriculturists could sell their products and services because the number of tourists would increase, if the visitors of an event stay to sleep at the venue. From the perspective of conservators, the pros regard relieving the state budget for maintenance although the key question is will it be enough to allow economic sustainability. The negative aspects of the model could be reduced by collaboration and good model management.

Conclusions
The indoor camping model implemented in heritage buildings aims to reconcile tourism business and heritage protection by providing economic fund necessary for the maintenance of buildings where it is based. Affirmation and revitalisation of fortifications brings a series of advantages, of which the most important is preservation, with adequate maintenance, presentation and use. By conversion of the fortifications, while preserving all important features, their stratification is emphasised, as well as their flexibility of purpose and uniqueness of ambience, so that their former defence function remains recorded in the structure and imported functions facilitate new dynamics of use, directed towards tourism and valorised through innovative programmes and models of their use. In so doing, fortifications should be perceived through a complex integrity, taking into consideration the purposes and facilities in the surrounding areas of fortifications themselves, as well as the natural and architectural specificities of each particular fortification, with the aim of complementing the natural, historical and cultural values of that tourism offer.
The research showed that the implementation of indoor camping in heritage buildings is not only possible, but preferable in case it is applied correctly: it should follow the conservators' requirements and the needs of a specific location, space and history heritage, as these structures are unique and thus demand an individual approach. A framework of an adequate implementation of indoor camping in protected heritage buildings represents the main contribution of this research, alongside with the perceptions of relevant stakeholders of a local case study. This model could be of interest both to academia and practitioners, as seen on the example of the municipality of Svetvinčenat (Croatia) interested in the concept. The limitations of the research steam from its local context and choice of the interview method, although the paper stresses the need of an individual approach to each implementation along with the inclusion of key stakeholders. The replication of the research in different countries could help overcome this issue and, at the same time, represents a suggestion for future research.
The exploration of tourist demand, predominantly youth segment shown that youth consumers value sustainability and heritage and are ready to pay higher price for accommodation in structures that promote this type of accommodation. Although the limited budget is the general characteristic of economic power of youth segment and they claim that the price is very important (57.72%) they do not chose the cheapest price option (73.5%). When considering the motif of experience and adventure (85.29%) that is highly regarded in context with experience of unique historic location (75.49%) and affirmation of sustainability (56.85%). These results contribute to knowledge that although the primary choice of staying in indoor camping in heritage building is event that attracted them to the location, the education level and recognition of heritage context of built structure is highly valued and appreciated. For its preservation and future sustainable use, the consumers (62.8%) are ready to pay higher prices that would be reinvested in further sustainable initiatives dealing with heritage preservation and use. The benefits are both for users and local community where the heritage is located are evident; new experiences combined with heritage in use and preservation. That leads to conclusion that the sustainable use of heritage building through indoor camping accommodation concept is desirable accommodation product and its competitiveness is high.
Recognising the possibilities of indoor camping is important for historic valorisation and entrepreneurship enhancement. The multiplicative effect affects many entrepreneurs who profit from the increase in tourist arrivals, in accordance with sustainable tourism development. The local Government, the private sector and the locals themselves will have benefits from indoor camping implementation, as recorded in the interviews with relevant stakeholders of the selected case study. In this paper, the possible implementation is elaborated on the possibility of application of indoor camping on the example of the most famous castle in Istria, the one in Svetvinčenat. There, the most suitable business model would be a public-private partnership and they were more interested in a longer operative period of the indoor camping but without interrupting nor interfering the daily activities in the Morosini-Gimani Castle (for example weddings or the escape room activities). Among its managerial implications the issues of various other forms of partnerships, legal entity of the company and organisation should be further explored in order to maximise the effects of the sustainability agenda of a concrete tourism destination.
The temporality of tourism business in protected heritage facilities is a specific characteristic of indoor camping, allowing retention of the primary function of any building in which it is based. The current legal framework does not recognise such a multifunctional use of buildings, as urban zones are strictly predefined, thus limiting the operability of indoor camping only to tourist zones. In addition to the need for introduction of new legislation in order to be recognised as a category of accommodation alongside with e.g., hotels and camping sites (which represents the first, entry barrier of the practical application of this model), indoor camping calls for reconsideration of the static urban development plans of tourist destinations, which would allow tourism destinations to be more agile in their response to the needs of the turbulent tourist market. This research direction needs to be further explored and regulated along with the issues of energy efficiency.
The experience of sleeping in a cultural attraction is unique per se, not to mention the importance of safety and isolation from others in the Covid-19 era which is offered by large fortifications. Indoor camping which follows conservators' requirements is a non-invasive and flexible model that could be implemented in different heritage buildings, offering guests a one of a kind experience in line with sustainability.
Author Contributions: All authors contributed to the paper evenly. Conceptualisation: I.S., T.F., R.K.P., Methodology: R.K.P., I.S., Data Analysis: R.K.P., T.F., Writing: I.S., T.F. Revision of the manuscript and the final approval of the version to be published: all authors. All authors have read and agreed to the published version of the manuscript.
Funding: The publishing of this paper is financially supported by Juraj Dobrila University of Pula, Project Tourism Development and Impact on Destination and by the authors personally.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to size of a research.