## 1 Introduction  
Virtual reality techniques can be used for 3D visualization in geoinformation, and geological sciences [1, 2], where the virtual scenario (or landscape) can be based on open or ad hoc created geospatial datasets [3], including digital terrain/surface models and bathymetric data [4]. We focused our attention on key parts of virtual landscapes, the so-called virtual outcrops, which can also be called \"virtual geosites\" (VGs) as defined in a recent work [5]. In our work, VGs are 3D representations of surface geology [6, 7] that are suitable for (i) popularizing geoheritage for a general audience by highlighting active geoinvernmental processes and (ii) engaging the young audience, which is particularly interested in cutting-edge forms of communication [8]. For the sake of clarity, in the following sections, we will use the term VG exclusively, as defined in [5]. As stated above, VGs may be regarded as particularly suitable for showcasing the geological heritage, or geoheritage, of a certain area. Geoheritage has been described and discussed in several papers during the last two decades [7; 9; 10; 11; 12; 13; 14; 15]. Geoheritage is strictly related to geological heritage sites or geosites. These can be regarded as elements of the geosphere, which can contribute to a better knowledge and understanding of Earth's history; they are also geological features, marked by a cultural, scientific, social, aesthetic, and economic value [16]. Geosites can be both geological and geomorphological features [17] and may be individual outcrops, mines, caves, tectonic structures, and volcanic landforms [18]. On the basis of their features, geosites can have local, regional, or global importance [19]. They also can be characterized based on their appearance: they may be outcrops, faults, and dikes, or isolated mountain peaks. It is worth noting that they can be subdivided into two categories based on whether they are active features/processes or inactive ones. During the last twenty years, many authors have focused on assessing geosites utilizing a wide gamut of criteria. Almost all assessments make use of the scientific value [20], made of three categories: representativeness, uncommonness [21], and the level of knowledge about the geosite, represented by published papers [15]. Representativeness regards how a geosite is representative of the geological phenomena that may be observed there. Concerning uncommonness, this represents how a geosite is uncommon at the local or worldwide level [21]. Furthermore, other values, which are \"additional\" [22; 23], can be identified and determined: cultural, ecological, aesthetic, economic, and educational values. Among these, it is worth mentioning the educational one, which [15] is composed of a few aspects: educational potential (how easily the lay public can understand the features of a geosite), accessibility, and safety. The present paper aims to showcase nine virtual geosites (VGs) belonging to the Santorini volcanic complex, representing a stunning volcanotectonic environment, the result of multiple caldera collapses associated with major explosive activity [24], using both VR applications and web-based GIS technologies. Web-based GIS platforms have succeeded in enhancing data access and dissemination, spatial data exploration, and visualization capabilities and provide additional options for processing, analyzing, and modeling available datasets [25]. This has led to the ever-increasing popularity of WebGIS in various fields. Several initiatives have previously utilized WebGIS functionalities to promote areas of interest and boost their tourism attractiveness. Using dynamic and interactive web-based maps to promote tourism resources [26], utilizing a participatory WebGIS platform to stimulate the promotion of a historical city center [27], and designing a narrative-oriented web map to showcase a geosite [28] are only a few of the numerous relevant applications. Moreover, ref.