Intangible Cultural Heritage in Tourism: Research Review and Investigation of Future Agenda

: Intangible cultural heritage (ICH) can be a valuable tourism resource for both government and local communities. However, the complex deﬁnition and the massive and fragmented nature of ICH data make it hard to review and conclude research trends and future directions of ICH tourism. In this study, 85 keywords extracted from ICH deﬁnitions are input in the Web of Science database before collecting papers indexed in the Social Sciences Citation Index, the Arts and Humanities Citation Index, and the Conference Proceedings Citation Index-Social Science and Humanities. Later, a systematic literature review of 418 ICH tourism studies from 76 countries published between 2000 and 2021 were conducted based on three groups of questions. The ﬁndings mainly illustrated that: (1) Currently research in ICH tourism is mainly composed of three themes: resource planning and sustainability, the impact of tourism development, and tourist behavior and destination marketing; (2) topics related to food tourism, sacred knowledge, traditional management systems, traditional management systems, legends, and myths can achieve high impact; (3) in the last ﬁve years, scholars have reduced using the ofﬁcial full name of ICH in tourism studies, while the category of “social practices, rituals and festive events” has become a hot topic since 2010; (4) ecotourism, culinary tourism, festival tourism, and religious tourism are the most discussed in ICH tourism research, and they will still be intensive topics in near future; (5) future directions in ICH tourism research are resultant of three vectors: place making, technology, and environment. The results present a comprehensive picture of current popular ICH topics and predict future directions in the ﬁeld of ICH tourism. The systematic review of literature can help contribute to both theoretical construction, heritage preservation, and tourism practices.


Introduction
The significance of intangible cultural heritage (ICH) has been widely recognized from the perspective of both cultural diversity and destination marketing. Despite the title containing "intangible", ICH not only includes immaterial elements, such as practices, representations, expressions, knowledge, and skills, but also has tangible sides of instruments, objects, artefacts, and cultural spaces [1]. This increases the difficulty of concluding the previous research statues in ICH tourism.
Currently, nationalistic understandings still dominate the ICH field, and official institutions are often responsible for the cognization and inscription of ICH [2,3]. In 1989, the United Nations Educational, Scientific and Cultural Organization (UNESCO) adopted the first specific international legal instrument on ICH, namely the Recommendation on the Safeguarding of Traditional Culture and Folklore [4], and the scope is very limited since the concept of "folklore" is more restrictive than ICH [5]. Later in 2003, UNESCO declared that there are five domains of ICH: oral traditions and expressions, including language as a vehicle of the intangible cultural heritage; performing arts; social practices, rituals, and festive events; knowledge and practices concerning nature and the universe; and traditional craftsmanship [1]. After this, governments and scholars in many countries began to promote this new form of "immaterial" or "living" culture, and governments worldwide now compete to have their countries' ICH inscribed by UNESCO [2]. For instance, the National Heritage Board of Poland (NHBP) announced the ICH list in six domains following UNESCO's criteria, and these domains include: social and cultural practices; oral traditions and literature; oral history and traditions, including language; performance and musical traditions; knowledge and skills related to traditional crafts; knowledge and practice concerning nature and universe [6]. Although China has registered most ICH in UNESCO, ICHs are classified into more specific catalogs in the list published by the Central People's Government of the People's Republic of China (CPGPRC): traditional oral literature and the language as its vehicle; traditional art, calligraphy, music, dance, drama, folk art, and acrobatic; traditional technique, medicine, and calendar; traditional etiquette, festival, and other folk customs; traditional sport and entertainment; and other intangible cultural heritage [7]. These domains are more applicable in tourism development with these descriptions, but it excludes some ICH types which are not suitable in economic practice.
When economic pressure and weakened practice are threatening some endangered ICHs [8], researchers regard tourism development as an effective solution for the survival dilemma of ICH [9,10]. For example, as United Nations World Tourism Organization (UNWTO) concludes, bundling tourist attractions to create themed sets, using existing circuits or reviving heritage networks, such as pilgrimage routes, festivals, and events are effective ways to produce popular ICH tourism products and destinations to attract tourists [11]. Although ICH has become a valuable tourism resource for both governments and local communities, there is still no clear definition of the question "what is ICH tourism?". From the perspective of attraction, ICH tourism has been viewed as "tourism centered on ICH resources and ICH destinations" [12]. From the perspective of tourists' interests and motivations, ICH tourism is "visiting ICH attractions and obtaining cultural experience" [13,14]. Furthermore, cultural tourism [15] and heritage tourism [16] are more popular definitions covering the meanings of ICH tourism. Similarly, some scholars identified the elements of creativity that help sustain ICH and creative tourism is arguably a solution for serial ICH [17]. In addition, large amounts of publications in the field of tourism with specific ICH are unidentified or unrecognized as ICH tourism by scholars, making it more difficult to review the current research trend of ICH tourism.
Although the definition of ICH tourism is vague, the major research trend of cultural tourism has shifted from tangible to intangible heritage [18]. For instance, ICH tourism is closely related to a sense of place [19,20], which is a window of opportunity in place making topics. Moreover, ICH tourism does not stay alone in fast-changing modern society and scholars try to connect it with some popular trends. For example, technology has brought a lot of changes and challenges for the preservation of ICH and the development of the tourism industry [21]. Besides, ICH is important for the sustainability of heritage sites, and its fundamentals are deeply rooted in places and communities, which represent critical factors for forming new global and competitive scenarios [17,22]. Specifically, ICH, such as indigenous knowledge, can also improve natural environment conditions [23].
Nevertheless, the complex definition, the massive and fragmented nature of ICH data, and scholars' acceptance of ICH tourism make it hard to review and conclude the current research status of ICH tourism. Therefore, further extraction and summary are needed in concluding the research trend and future direction of ICH tourism. Reviewing the current research status of ICH tourism thus enables this study's theoretical value and practical importance. This paper aims to identify core concepts and research trends and ascertain the topic orientation of ICH tourism. To reach the object of this study, three groups of questions are proposed. The first group of research questions is about the general description of data, including: When were the publications published? Which countries are these ICHs from? The second group of research questions is based on the frequency Land 2022, 11, 139 3 of 21 of journals, conferences, and articles, including: Which journals and conferences are these papers from? Which papers have the highest citations? Most importantly, the third group of research questions emphasizes this study, including: What is the main research content? Which research methods are used? What are the current popular topics and future trends of ICH tourism? In this paper, a systematic review consisting of three steps is conducted. Firstly, this article presents the methods used to collect all the relevant and high-quality papers both in journals and conference proceedings to perform the review. A total of 85 keywords extracted from ICH definitions of UNESCO are input in the Web of Science (WOS) before collecting papers indexed in the Social Sciences Citation Index (SSCI), the Arts and Humanities Citation Index (A&HCI), and the Conference Proceedings Citation Index-Social Science and Humanities (CPCI-SSH). Secondly, the geographic and yearly distribution of articles is illustrated. Thirdly, current research contents and methods are clarified, which is followed by the analysis of highly cited articles, journals, and conferences. Finally, research trends and future directions in ICH tourism are proposed. This study explores a wide range of definitions of ICH to collect previous tourism studies and provides other researchers with useful references, such as choosing ICH relative topics, degerming research directions, and methods.

Process of Data Collection
In this study, the literature review methodology was used to discuss the current status of ICH tourism research, and WOS was chosen as the data source, which has the longest period of published scientific papers covering most scientific disciplines. In this database, the authors selected journals indexed by SSCI, A&HCI, and CPCI-SSH to ensure the quality of selected articles. Among them, publications on SSCI and A&HCI journals are regarded as the standard of research achievement in the social sciences and humanities, due to the reason that journals on SSCI and A&HCI lists usually have a blind peer-review process, good operations, and citations data [24,25]. Besides these two indexes, scientific conference papers have the characteristic of reflecting the leading edge of the discipline as an important supplement to the journal literature. Therefore, this study also collected articles indexed by CPCI-SSH, where we can get to know the emergence and development of the latest concepts.
First of all, to collect articles on WOS, it is necessary to identify the searching keywords. This literature collection process began with researching articles on the "intangible cultural heritage tourism" topic. Besides this topic, the definition and detailed description of ICH from UNESCO was adopted in this research to make sure the literature can cover as many types of ICH as possible. Therefore, this study confirmed 85 searching keywords of ICH classified into six categories, including: intangible cultural heritage; oral traditions and expressions, performing arts, social practices, rituals, and festive events; knowledge and practices concerning nature and the universe, and traditional craftsmanship (shown in Table A1). To make sure the data is in the field of ICH tourism instead of other scopes, the term "tourism" was added after each ICH keyword. 1667 results came out by searching these six groups of keywords before 1 July 2021. In the second step, the two researchers worked independently to exclude articles that are not related to ICH tourism by reading abstracts and the results show that there are 479 papers relative to the topic. For the last step, 61 repeated articles were deleted and only 418 results were left for analysis (the selection process is shown in Figure 1).

Data Analysis
In the data analysis process, articles were identified, categorized, and synthesized to review research trends and future directions. Three groups of research questions are analyzed. The first group of research questions is about the general description of data, including: When were the publications published? Which countries are these ICHs from? The second group of research questions is based on the frequency of journals, conferences,

Data Analysis
In the data analysis process, articles were identified, categorized, and synthesized to review research trends and future directions. Three groups of research questions are analyzed. The first group of research questions is about the general description of data, including: When were the publications published? Which countries are these ICHs from? The second group of research questions is based on the frequency of journals, conferences, and articles, including: Which journals and conferences are these papers from? Which papers have the highest citations? Most importantly, the third group of research questions emphasizes this study, including: What is the main research content? Which research methods are used? What are the current popular topics and future trends of ICH tourism?

ICH Category Analysis
An overview picture of articles collected after three steps shows that 128 papers are from the definition of "intangible cultural heritage", followed by the oral traditions and expressions category with the number 78. There are 73 articles from the category of "social practices, rituals, and festive events", 62 articles from the category of "knowledge and practices concerning nature and the universe". Also, performing arts and traditional craftsmanship only account for 50 and 27. The category constitution of collected papers is shown in Figure 2.

Spatial-Temporal Characteristic of ICH
There has been a growing body of research in ICH tourism, with an increase from 2 publications in 2000 to 418 publications until July 2021. According to search results, the earliest paper in the WOS was published in 2000, three years before UNESCO [1] proposed the definition of "intangible cultural heritage". As Figure 3 shows, in the first ten years, most studies focused on the category of "Oral traditions and expressions". Later, more studies appeared on the topic of general ICH, when traditional craftsmanship stayed as the most unpopular type of ICH in tourism activity. The cutoff date for the publications identified and reported on in this paper was on the first day of July and this may be the

ICH Category Analysis
An overview picture of articles collected after three steps shows that 128 papers are from the definition of "intangible cultural heritage", followed by the oral traditions and expressions category with the number 78. There are 73 articles from the category of "social practices, rituals, and festive events", 62 articles from the category of "knowledge and practices concerning nature and the universe". Also, performing arts and traditional craftsmanship only account for 50 and 27. The category constitution of collected papers is shown in Figure 2.

Spatial-Temporal Characteristic of ICH
There has been a growing body of research in ICH tourism, with an increase from 2 publications in 2000 to 418 publications until July 2021. According to search results, the earliest paper in the WOS was published in 2000, three years before UNESCO [1] proposed the definition of "intangible cultural heritage". As Figure 3 shows, in the first ten years, most studies focused on the category of "Oral traditions and expressions". Later, more studies appeared on the topic of general ICH, when traditional craftsmanship stayed as the most unpopular type of ICH in tourism activity. The cutoff date for the publications identified and reported on in this paper was on the first day of July and this may be the cause of the apparent dip in the number of papers in 2021.  From the spatial perspective of collected papers, the geographical distribution of ICH tourism cases from six continents, namely Asia, Africa, North America, South America,    From the spatial perspective of collected papers, the geographical distribution of ICH tourism cases from six continents, namely Asia, Africa, North America, South America,  From the spatial perspective of collected papers, the geographical distribution of ICH tourism cases from six continents, namely Asia, Africa, North America, South America, Europe, and Australia, were analyzed by using ArcGIS (shown in Figure 4). Numerous types of ICHs in 76 developing and developed countries, such as Canada, United States, the Netherlands, Poland, Japan, China, Australia, Malawi, Ecuador, and Jamaica, can enable this study to consider the effects of different ICH in different regions. Although some countries do not have advanced academic conditions, researchers from developed countries still noticed the precious value of local ICH as tourism resources. Overall, the spatial-temporal distribution of collected papers ensures this study has enough samples in various regions to conclude the current research trend. Europe, and Australia, were analyzed by using ArcGIS (shown in Figure 4). Numerous types of ICHs in 76 developing and developed countries, such as Canada, United States, the Netherlands, Poland, Japan, China, Australia, Malawi, Ecuador, and Jamaica, can enable this study to consider the effects of different ICH in different regions. Although some countries do not have advanced academic conditions, researchers from developed countries still noticed the precious value of local ICH as tourism resources. Overall, the spatialtemporal distribution of collected papers ensures this study has enough samples in various regions to conclude the current research trend.

Main Themes in ICH Tourism
Concluded from these collected publications, three themes dominated previous ICH tourism research in general. Most studies focused on three directions: resource planning and sustainability, the impact of tourism development, and tourist behavior and destination marketing. These three dimensions are connected and be impacted by each other.

Resource Planning and Sustainability
The process of planning and developing ICH tourism begins with detecting and protecting resources. The special trait of intangible heritage is that it can be easily influenced by local people and social change and can determine the fragile characteristic of resources. Therefore, while planning ICH tourism, challenges and potentials of resources are appearing at the same time, which requires communities, governments, and planners to balance the relationship between ICH protection and tourism development. For example, in constructing and safeguarding ICH level, Maria Katelieva and her coauthors [26] discussed UNESCO's influence in heritage-making, valorization, and the prioritizing of certain domains and thus increasing their chance for tourism utilization. Most of the interviewed experts criticized the process or questioned the advantages of the ICH list and the safeguarding policy of UNESCO. They argued that there should be a differentiation between practiced and UNESCO ICH since only the elements on the list are perceived as a valuable

Main Themes in ICH Tourism
Concluded from these collected publications, three themes dominated previous ICH tourism research in general. Most studies focused on three directions: resource planning and sustainability, the impact of tourism development, and tourist behavior and destination marketing. These three dimensions are connected and be impacted by each other.

Resource Planning and Sustainability
The process of planning and developing ICH tourism begins with detecting and protecting resources. The special trait of intangible heritage is that it can be easily influenced by local people and social change and can determine the fragile characteristic of resources. Therefore, while planning ICH tourism, challenges and potentials of resources are appearing at the same time, which requires communities, governments, and planners to balance the relationship between ICH protection and tourism development. For example, in constructing and safeguarding ICH level, Maria Katelieva and her coauthors [26] discussed UNESCO's influence in heritage-making, valorization, and the prioritizing of certain domains and thus increasing their chance for tourism utilization. Most of the interviewed experts criticized the process or questioned the advantages of the ICH list and the safeguarding policy of UNESCO. They argued that there should be a differentiation between practiced and UNESCO ICH since only the elements on the list are perceived as a valuable heritage, when the UNESCO experts believed that with the UNESCO label destinations can attract more influential actors in terms of economic, social, or political issues, and this can result in a strong intervention in the tourism [26]. At the national level, Junjie Su [10] studied the perspectives of officials from national to local levels in regard to the relationship between protection and commodification of the ICH in a popular heritage tourism area in China; Research results illustrate the diversity and stratification of the officials' perspectives. When the national ICH policy exerts profound influence in a top-down manner, local officials are more sympathetic to the tourism commodification of ICH. To plan ICH tourism, Minoo H. Esfehani and Julia N. Albrecht [27] identified two sets of factors that affect related tourism planning, the perceived appropriateness of ICH for use in tourism and the accessibility of ICH-based tourism products for visitor markets. In previous studies, from international policy making to local tourism development, undoubtedly attach great importance to the sustainability of heritage protection and economic development.
The discussion on the authenticity of heritage has never stopped in recent years. When heritage is affected by interests in the tourism industry, it is easy to cross the boundaries of authenticity and become inauthentic. Many studies have explored the authenticity of indigenous heritage in China. When studying the local ICH in tourism commodification from music players' perspectives, Junjie Su [28] believed that a discussion of the tension between protection and commodification of heritage will usually incur the discussion of authenticity. Similarly, Dawei Li and Shangyi Zhou [29] discussed the authenticity of Naxi music from the perspective of musicians, and the results find out local music scenes under tourism do not follow the mirror image of tourists blindly and pay attention to music and their own development. Besides the perspective of player or performer, [30] examined how the authenticity of craftsmanship heritage is planned and staged in the cultural museum context by providing tourists an authentic experience through combing the tangible and intangible forms, such as object display, modern exhibition technology, simulated environment, and living processes of craftsmanship showcases. However, Wasana S. Handapangoda and her coauthors [31] believed that authenticity was an evolving concept of search and discovery and its meanings are numerous, contradictory, and irreconcilable. Therefore, the boundary between "authentic" (real) and "inauthentic" (fake) was non-existent, so "boundary crossing" was a matter of (re)presentation. The discussion of authenticity in ICH tourism is still going on and this is an important basis for the sustainable development of ICH tourism.
Besides discussions on the authenticity problem, to accommodate ICH, both social changes and the tourism industry, the sustainability problem of heritage has attracted many authors' attention. In 2000, three years before UNESCO proposed the definitions and domains of ICH, Matthew Krystal [32] discussed the conversion of the Moreria Nima' K'iche' (a small business that fabricates and rents the costumes, props, and masks used in traditional dance-dramas) and how the resulting institution accommodates both cultural revitalization and tourism. He illustrated that the most significant change has been the effort to make tourism an important way to subsidize the activities of the Moreria. This is an early exploration of how ICH can achieve sustainability by developing the tourism industry. Some scholars believed that assessment needs to be conducted in ICH tourism to achieve sustainability. For example, market value [33], interest distribution mechanisms [34], social networking practices [35], and cognition values by ICH inheritors [36]. With the development of modern technology, Yanling Zhang and Huicun Tan [37] stressed that big data analyses can expand tourism-based inheritance modes of intangible cultural heritages, creatively develop cultural tourism products, and choose suitable modes for tourism-based protection and inheritance of intangible cultural heritages by internet thinking.

The Impact of Tourism Development
Physical change is the most direct impact brought by the tourism development of ICH. Many special landscapes, products, and activities are created based on ICH. For example, Fang Xu [38] put forward some means and strategies to develop ICH tourism by designing the opera grand theatre, square, folk village, staged scenery, and hotel, which are designed based on the Neixiang Wanbang Opera. One example can be seen in reconstruction after the earthquake when Christiane Brosius and Axel Michaels [39] illustrated that reconstruction is connected to ethnicity, nation, and citizenship, as well as social, symbolic prestige, economic status, and distinction. Besides these, ICH can also improve natural environment conditions. For instance, Nian Wang and his coauthors [22] discussed the mechanism of the influence of indigenous knowledge systems on landscapes through natural resource management and proposed an ideal diagram of the sustainable landscape of the rice terraces. Similarly, Hu Tang [23] discussed the indigenous knowledge of local Naxi ethnic people applied to protect the water resource. In conclusion, these impacts discussed by researchers are mainly positive.
Stakeholders, such as performers, inheritors, local residents, and the government can gradually be impacted during tourism development. Place attachment or person-place bonding [19] has become a popular topic when strengthening local pride and sense of identity is the most significant phycology change of local people. For example, diaspora language in Mexico, and indigenous languages [40] in Canada and Italy [41] were detected to foster cultural bonds, local pride, and a sense of identity in tourism development. Besides language, social practices, rituals, and festive events, such as religion and food, can also create a connection between people and places. For instance, Leigh K. Mercer and H. Rosi Song [42] recognized the firm linking of food and identity in Spain, where gastronomy and tourism have ultimately helped strengthen the region's broader political and cultural recognition abroad. Another perspective of inheritor and practitioner, tourism can result in economic benefits for performers and improving self-esteem as cultural custodians [43].
Not only does the tourism development of ICH impact places and people, but also makes an impact on ICH itself. Without the border, the judgment of commercialization, and authenticity, ICH can be changed in negative ways. For example, based on ethnographic fieldwork among spirit mediums and their followers in Vietnam, Gertrud Hüwelmeier [44] argued that the heritagization of spirit mediumship and its reenactment in state-sponsored theaters results in de-contextualization and aesthetic flattening. Similarly, Ruwan Ranasinghe and Li Cheng [45] argued that Vedda are susceptible to the influence of mobilities within and without indigenous tourism practices, and indigenous cultural tourism causes a loss of inherited meaning of their cultural values. Therefore, planners should realize and balance the significance of distinctive heritage parallel to commercial gains of tourism.

Tourist Behavior and Destination Marketing
Measuring and predicting tourist behavior are essential in designing popular ICH tourism. Many scholars have conducted studies in cognition [9], attitude [9], visiting intention [9,46], demand [47], motivation [48,49], and satisfaction [50]. For instance, Qihang Qiu [9] and her coauthors surveyed 368 residents and conducted path analysis to test tourist behavior, and findings revealed significant positive correlations between residents' cognition of ICH value, their attitudes, and travel intentions. These studies have detected direct and indirect relationships between tourist behavior and ICH tourism, which can contribute in both practical and theoretical ways.
Creating image and branding ICH concepts of different places are new strategies to marketing tourist destinations. These images are mainly positive. For instance, the Santa place myth is built on the social construction of Santa's winter home replete with snow, pine trees, and reindeer [51]; happiness, spirituality, and cultural authenticity are prominent factors in Bhutan's tourism image, resulting from traditional festivals and religion [52]. On the contrary, Smaranda Cosma and her coauthors [53] tried to find an answer to the controversial question of whether the Dracula myth should be used as a brand promoting Romania as a tourist destination. Although many scholars have studied the destination image created by ICH tourism, more details in place making functions are needed.

Highly Cited Topics
Among authors of these 418 articles, Chinese scholars account for a large proportion. For instance, Mu Zhang, a scholar from Jinan University, has published more than seven articles indexed in SSCI after obtaining funds related to ICH research.

Topic Analysis for Journal Papers
Among the collected data, this study summarizes the top 10 journals that published the most ICH tourism related articles (shown in Table 1). Resulting from the fragile nature of ICH and scholars' attention, the journal "Sustainability" published most ICH tourism articles (31). Besides this, most journals are indexed in SSCI and mainly publish articles in the field of tourism.  According to the data collected on the WOS database, the top 10 journal papers are ordered by citation score (shown in Table 2). These citation numbers range from 244 to 47. Three of these highly cited articles are from Tourism Management and two of the highly cited articles are from Annals of Tourism Research. From the perspective of research topics, five articles with the highest citations were studying food tourism or culinary traditions in tourism. Furthermore, these five articles were both published by well-known journals in the tourism field, namely Tourism Management, Annals of Tourism Research, Journal of Sustainable Tourism, and International Journal of Hospitality Management. Moreover, besides the topic of food tourism or culinary tourism, research related to sacred knowledge, traditional management systems, traditional management systems, legends, and myths also gained very high citations.

Topic Analysis for Conference Proceedings
Although there are 262 journal articles, only 156 conference articles were analyzed in this study, and very few conferences have produced more than 2 articles related to ICH tourism (shown in Table 3). These six conferences were located in Portugal, Greece, China, Croatia, Bulgaria, France, and Singapore. Among them, the International Scientific Symposium on Economy of Eastern Croatia-Vision and Growth, the International Multidisciplinary Scientific Conference on Social Sciences and Arts, and the International Conference on Education and Education Management have been organized for several consecutive years. The most popular conference in ICH tourism, International Conference on Heritage and Sustainable Development, focused on heritage and sustainability, while other conferences focused on social science, education, economy, and tourism. The top 10 conference proceeding papers are ordered by citation score (shown in Table 4); these citation numbers range from 25 to 4, which is far less than journal papers. Similar to high-indexed articles from journals, three of the high-indexed conference articles are on the topic of gastronomy and traditional culinary in tourism. Beside these, the general term of "intangible cultural heritage" was more frequently mentioned in titles.  Qualitative and quantitative methods including literature analysis [29], questionnaire surveys [9], social media research [73], performance analysis [29], participation observation, interviews [29,41], case studies [74], and ethnographic field research [27,44] are conducted frequently in ICH tourism research, together with using content analysis with qualitative data [54,73] and using statistical methods to analyze quantitative data [9]. The combination of interview and content analysis for paraphrasing and reducing text is one of the most popular methods in ICH tourism. For instance, Maria Katelieva [26] and her coauthors collected 25 semi-structured interviews with experts from different organizations including UNESCO, academic, Ministry of Sustainability and Tourism, Destination management organizations (DMOs), NGOs, museums, relevant departments of the provincial government of Lower Austria, and knowledge bearers. In previous studies, scholars adopted qualitative methods more than quantitative methods. This preference can be changed in recent years when factor analysis, cluster analysis, path analysis, the structural equation model, etc. are conducted to find more people-place bonding.

Research Trend
From 2000 to 2021, scholars showed a different attitude in using terms of "intangible cultural heritage", "oral traditions and expressions", "performing arts", "social practices", "rituals and festive events", "knowledge and practices concerning nature and the universe", and "traditional craftsmanship". By using Bubblelines analysis in Voyant Tools, the frequencies of those terms appearing in previous literature change based on different topics in each domain (Bubblelines are shown in Figure 5). Firstly, the adoption of the title "intangible cultural heritage" in tourism research was after 2006, and later an explosion of using this title can be found between 2011 and 2015. However, in the last five years, scholars have reduced using the official full name of ICH in tourism studies. Secondly, although the theme of "oral traditions and expressions" is not as popular as other categories, studies have been conducted on oral expression, tales, legends, myths, songs, poems, and drama, etc. Among them, myths and legends are relatively common topics in tourism development. Thirdly, "performing arts", which is more popular than "oral traditions and expressions" in tourism research, simply attracted scholars by performance. Fourthly, the category of "social practices, rituals, and festive events" has become a hot topic since 2011. In this domain, a large number of tourism resources are included, such as social practices, rituals, festivals, worship, rites, traditional games, traditional sport, ceremonies, traditional patterns, traditional food, fishing, religion, etc. According to the Bubblelines analysis, "social practices, rituals, and festive events" is a particularly popular topic in tourism research in these past five years. Fifthly, the category of "knowledge and practices concerning nature and the universe" includes a large number of tourism resources of ICH such as wisdom, beliefs, shamans, indigenous knowledge, etc. In this category, tourism research topics related to indigenous knowledge and ecology tourism have attracted scholars' attention mostly. Finally, "traditional craftsmanship", which has relatively limited articles in the field of tourism, stayed cold for the past 20 years, although it can bring economic benefit to the local community. of using this title can be found between 2011 and 2015. However, in the last five years, scholars have reduced using the official full name of ICH in tourism studies. Secondly, although the theme of "oral traditions and expressions" is not as popular as other categories, studies have been conducted on oral expression, tales, legends, myths, songs, poems, and drama, etc. Among them, myths and legends are relatively common topics in tourism development. Thirdly, "performing arts", which is more popular than "oral traditions and expressions" in tourism research, simply attracted scholars by performance. Fourthly, the category of "social practices, rituals, and festive events" has become a hot topic since 2011. In this domain, a large number of tourism resources are included, such as social practices, rituals, festivals, worship, rites, traditional games, traditional sport, ceremonies, traditional patterns, traditional food, fishing, religion, etc. According to the Bubblelines analysis, "social practices, rituals, and festive events" is a particularly popular topic in tourism research in these past five years. Fifthly, the category of "knowledge and practices concerning nature and the universe" includes a large number of tourism resources of ICH such as wisdom, beliefs, shamans, indigenous knowledge, etc. In this category, tourism research topics related to indigenous knowledge and ecology tourism have attracted scholars' attention mostly. Finally, "traditional craftsmanship", which has relatively limited articles in the field of tourism, stayed cold for the past 20 years, although it can bring economic benefit to the local community. While the frequency of mentioning "intangible cultural heritage" in tourism research has decreased in the past five years, four topics are particularly eye-catching, namely ecotourism, culinary tourism, festival tourism, and religious tourism (Bubblelines are shown in Figure 6). match terms that start with this word as one term. Source: edited by authors based on research and Voyant Tools output.
While the frequency of mentioning "intangible cultural heritage" in tourism research has decreased in the past five years, four topics are particularly eye-catching, namely ecotourism, culinary tourism, festival tourism, and religious tourism (Bubblelines are shown in Figure 6). As the most inconspicuous ICH domain, knowledge and practices concerning nature and the universe, are often overlooked in planning and marketing places. However, indigenous knowledge sometimes plays an essential tool to attract tourists who aim to experience ecological senses and perceive harmony between humans and nature. This trend is more obvious when some countries pay attention to rural development and promote the harmonious development of man and nature. The knowledge can be found in residential buildings, agricultural facilities, water resource protection, and medical care. For example, in Southwest China, local indigenous knowledge systems of rice farming methods and livelihoods have influenced spatial patterns of natural resource management, such as mountains, forests, water, and agricultural resources [22]. Therefore, ecotourism related to knowledge and practices concerning nature and the universe becomes the central issue in recent years.
The ICH domains of social practices, rituals and festive events can provide many types of tourism activities and among them, culinary tourism, festival tourism, and religious tourism are popular research fields. Culinary tourism, a new phenomenon in the tourism industry all around the world [75], not only reflects local customs and natural resources, but also becomes a popular attraction itself. For example, culinary events and food markets can both create attractive cities [76] and serve as a tool for cultural education and promotion of the entire region [77]. Some food with a long history in local places has developed a complete industry chain for visitors. For example, wine tourism in Portugal As the most inconspicuous ICH domain, knowledge and practices concerning nature and the universe, are often overlooked in planning and marketing places. However, indigenous knowledge sometimes plays an essential tool to attract tourists who aim to experience ecological senses and perceive harmony between humans and nature. This trend is more obvious when some countries pay attention to rural development and promote the harmonious development of man and nature. The knowledge can be found in residential buildings, agricultural facilities, water resource protection, and medical care. For example, in Southwest China, local indigenous knowledge systems of rice farming methods and livelihoods have influenced spatial patterns of natural resource management, such as mountains, forests, water, and agricultural resources [22]. Therefore, ecotourism related to knowledge and practices concerning nature and the universe becomes the central issue in recent years.
The ICH domains of social practices, rituals and festive events can provide many types of tourism activities and among them, culinary tourism, festival tourism, and religious tourism are popular research fields. Culinary tourism, a new phenomenon in the tourism industry all around the world [75], not only reflects local customs and natural resources, but also becomes a popular attraction itself. For example, culinary events and food markets can both create attractive cities [76] and serve as a tool for cultural education and promotion of the entire region [77]. Some food with a long history in local places has developed a complete industry chain for visitors. For example, wine tourism in Portugal can engage people with wine storytelling, wine tasting excitement, wine involvement, and winescape [78]. Similarly, cheese plays a critical cultural, historical, and tourist role in many places when cheese in the Netherlands communicates regional identity to visitors [79]. Festival tourism, an important way to increase the interactivity of destinations and consolidate the impression of local entertainment, can improve the perception of ritual and mystification when the participation of local residents and actors enriches the content of the festival. For example, in Bhutan, cultural sightseeing is the major travel motivation and religious festivals are among the primary contexts within which local people and tourists interact [80]. These events, which increase interactivity, enhance the unique cultural attraction of local places, create a strong atmosphere of national unity, and a clear image of local identity, thus becoming a research trend in ICH tourism. ICH can also create divine space, where the place is recontextualized with mythology or religion and the traditional value is protected. For example, Susan Dunn-Hensley [81] believed that, in a world increasingly disconnected from tradition and nature, many pilgrims come to the Shrine of Our Lady of Walsingham seeking a connection with both the past and the material present. Besides these spontaneous mythical destinations, a place can be interpreted in a novel, original way as a spiritual resource for tourists visiting the area, and for the local population [82]. As more tourists seek spiritual connection, religious tourism has become a hot topic in academia.

Future Direction
As concluded in the above section, ecotourism, culinary tourism, festival tourism, and religious tourism are the most popular topics in the previous studies. These types of tourism will still be intensive topics in the near future. However, more specific research questions need to be proposed.

Potential of Place Making
Compared with tangible cultural heritage, ICH was neglected during place making research. From performing arts, festive events, rituals, traditional craftsmanship, oral traditions, and knowledge of practices, ICH provides place making tools to improve places' aesthetics and attract tourists. It contributes to an understanding and enrichment of local history, identity, and ecology. During this process, ICH plays a key role in branding and marketing. When museums, theme parks, monuments, events, and souvenirs are transformed from ICH, they became a tool and scale mixed with tangible and intangible elements in place making. As part of the cultural landscape and sightseeing route, ICH can fulfill tourists' intentions to experience local knowledge and culture. However, previous studies mainly focused on destination branding and marketing, where the functions of tangible and intangible heritage were not classified clearly, hiding the real place making power of ICH. From this perspective, the image and emotion perceived from ICH deserve more research, and place making results within and without ICH elements should be clearer. For example, what is the role of ICH in place-making and placemaking? How does ICH contribute to tourists' cognition and emotion in the place making process? How do tangible and intangible heritages bring differences in place making? Future research in the ICH tourism field can try to solve these questions. Therefore, illustrating the power of place making in ICH tourism is one of the potential directions in this field.

Technology Interaction between Destination and Tourist
With the development of technology, the way of participation becomes more creative, and co-creation becomes more and more popular in ICH tourism. For example, Hyejin Park and her coauthors [83] investigated travelers' behavior to visit pilgrimage destinations and share experiences on social networking sites (SNS); the results show that because SNS provides a means to represent the self, travelers might work to create a favorable image or enhance their status by displaying their pilgrimage experiences on SNS. This phenomenon hence promotes and strengthens destination image imperceptibly in a specific direction when visitors display their experience. Judging from this development trend, pilgrimage tourism will be more sacred, because the user-generated content filters out other things unrelated to the theme of destination. Besides those popular social media, applications created by destination management offices, private companies, or researchers can also achieve the functions. For instance, Andrea Gomez-Oliva and coauthors [84] proposed an innovative and co-created application named "Be Memories" for tourists to spread the ICH in a Spanish village with huge cultural value during local festivities. The results show that social media can enable a local experience via agile, fresh, and crowd-sourced content that people enjoy. From this perspective, social media content is the low-cost and sustainable supplement to official information, documentaries, and local tours. Despite time and space constraints, it is used as a powerful auxiliary tool to create, recognize, understand, and present ICH images in tourism [73,85] In recent years, the environment topic has attracted scholars not only from geography and ecology disciplines but also in tourism management, economic, and political science areas. This trend is more obvious when climate change and extreme weather happen frequently and people's environmental awareness has been raised. Indigenous knowledge is thus connected with environmental concerns, and the potential to achieve the sustainability of local places. On one hand, indigenous knowledge is used in natural resource preservation [23], disaster adaptation [86], and wildlife and biodiversity conservation [87,88]. It will be realistic to seek some solutions from ancient people's wisdom, that is, solve environmental problems from indigenous knowledge. On the other hand, indigenous knowledge is also related to ecotourism [22,89], following global trends and strengthening the competitiveness of tourist destinations. When some countries emphasize their policy on rural development, ecotourism-based projects will also have a promising future. In general, the knowledge and practices concerning nature and the universe can act as a wide range and a long history system, including different views of the natural environment and the universe from various nations in the world. In the context of more discussion about environmental issues, the wisdom of some ancients can demonstrate value. For example, what implication can knowledge and practices concerning nature and the universe bring to the environment of destination? Generally, how do ICH and the environment influence each other? How do tourists perceive the indigenous knowledge in the destination? How are tourists influenced by indigenous knowledge and ecotourism? Therefore, the sustainability of the environment is also a starting point for future ICH tourism.

Conclusions
This article solved the problem of defining vague domains and complex explanations of ICH by writing a literature review and taking a look into high-quality articles indexed in SSCI, A&HCI, and CPCI-SSH. After defining what ICH tourism is and extracting 85 keywords from UNESCO's explanations of ICH, this study collected 418 journal and conference articles from WOS to analyze the current research trend and future direction of ICH tourism research.
Firstly, this review analyzed the temporal-spatial distribution of ICH tourism research. There has been a growing body of publications in ICH tourism, with an increase from 2 articles in 2000 to 418 articles until July 2021. ICH tourism in 76 developing and developed countries have been researched by scholars regardless of their nationalities. Secondly, this paper proposed that current research in ICH tourism can generally be found in three directions: resource planning and sustainability, the impact of tourism development, and tourist behavior and destination marketing. These three dimensions are connected and impacted by each other. Specifically, besides these three themes, topics of food tourism or culinary tourism, research related to sacred knowledge, traditional management systems, legends, and myths can gain very high citations. Those theories and methods used in previous studies can be frequently found in ethnographic, anthropological, folklore, and social science fields. Thirdly, in the past five years, scholars have reduced using the official full name of ICH in tourism studies. The category of "social practices, rituals, and festive events" has become a hot topic since 2010. In this domain, a large number of tourism resources are included such as social practice, rituals, festivals, worship, rites, traditional games, traditional sport, ceremonies, traditional patterns, traditional food, fishing, religion, etc. Specifically, four topics are particularly eye-catching, namely ecotourism, culinary tourism, festival tourism, and religious tourism. Fourthly, the potential of place making, technology interaction between destination and tourist, and sustainability of the environment are potentially popular research directions in the future.
From the theoretical perspective, this study proves the possibility of concluding overview pictures of ICH tourism by the five ICH domains of UNESCO. It identifies the difference of taking ICH elements as study cases in tourism research. These results suggest to other researchers the popular heritage types and potential topics regarding both the quality and quantity of collected literature. In heritage preservation and tourism practices, this study reminds planners of what scholars frequently researched regarding three problems. Firstly, the process of resource planning and sustainability begins from detecting resources, protecting heritage, and keeping the authenticity of ICH. Secondly, planners need to consider the impact of tourism development on stakeholders, such as performers, inheritors, residents, government, and ICH itself. Thirdly, ICH is a new strategy for creating a special image of a destination when it is essential for planners to know how to measure and predict tourist behavior and market destinations.
Although this literature review has an outbreak in identifying high-quality publications to analyze, we believe that the range of ICH is larger than 85 keywords. Also, as part of searching keywords, the terminology of "tourism" is too limited to conclude all the definitions and domains of activities in the tourism industry. Therefore, new review methods and different perspectives can be adopted to analyze different research trends and future directions. Secondly, this article was only reviewing English literature and large swathes of research are omitted due to this, which can cause the main flaw in the topic of ICH tourism. Hence, review articles in multiple languages are needed as supplements in ICH tourism.  Data Availability Statement: Data sharing is not applicable to this article.

Acknowledgments:
The authors express their sincere appreciation to Jacek Kotus and Michał Rzeszewski at Adam Mickiewicz University for their helpful comments and suggestions. Also, we appreciate the comments from three reviewers and editors.

Conflicts of Interest:
The authors declare no conflict of interest.