# X-Reality Museums: Unifying the Virtual and Real World Towards Realistic Virtual Museums
## 1 Introduction  
Culture is a major connecting tissue of a society, facilitating its links with the past, strengthening its members' bonds and elevating their quality of life, but also allowing them to envision and plan their future. Culture has gone through important changes, expanding its potential audience, and is currently in a revolutionary phase-named Culture 3.0-in which individuals are expected to assimilate and manipulate in their own way the cultural contents they are being exposed to [1]. Contemporary museums are challenged to not only adapt to the current status quo, and follow existing trends, but also shape future cultural experiences. Evolution though does not happen in isolation; instead it is easier when it is sought following multidisciplinary approaches. In this case, a discipline providing a helping hand is information and communication technologies (ICTs). The abundance of mature technologies in the fields of computer graphics, human-computer interaction, computer vision, etc., have dissolved reluctances, even of the most secptics, to harness digital tools with Cultural Heritage (CH) towards better understanding our history and civilization [2], as well as actively participating and disseminating our cultural heritage. Furthermore, in accordance with Culture 3.0, state-of-the-art technologies are expected to play an important role to enhance museums' on-site experiences and hence transform them into high-technological CH spaces [3], able to provide high quality interactive experiences to their audience. Museums take advantage of ICT technologies to exhibit digital content besides their physically exhibited artefacts and often employ augmented or virtual reality (collectivelyreferred to as \"mixed reality\") technologies to immerse visitors in novel experiences, following playful approaches [4]. These immersive technologies, however, have the potential to truly innovate museum experiences, beyond merely engaging visitors to artificial worlds. When used in combination, and by employing state-of-the art computer graphics, multisensory interaction, and artificial intelligence (AI) [5], they have the potential to orchestrate experiences of both physical [6] and virtual [7] worlds in an outstanding blend. Museum visitors can be immersed in virtual worlds unravelling in front of them and substituting in a seamless manner the museum's physical environment. Virtual agents in this new world will behave and move naturally, thus acquiring the potential to directly interact with visitors who will be transformed from passive viewers to keen participants. The presented work elaborates on the aforementioned vision and discusses background information and required technological advancements to attain it. In particular the contributions of this work are: (i) a conceptual model that can be used as a reference for implementing XR museum experiences which transcend the boundaries between real and virtual interaction in the museum space, (ii) the elaboration of a novel approach, that of \"true mediated reality\", which refers to the collective technologies in support of realistic, high-quality human-to-virtual character interactions in cultural heritage contexts, (iii) a tangible case study, illustrating how the proposed conceptual model is materialized. The rest of this article is structured as follows. Section 2 presents a review of the literature, introducing readers to the extended reality (XR) concept, as well as the current state regarding the technological components involved in the proposed conceptual architecture (diminished reality, true mediated reality, and natural multimodal interaction), concluding with a highlight on future research directions. Section 3 elaborates on the proposed conceptual model for building unified XR experiences toward realistic virtual museums, providing a segmentation of the components into a layered design so as to facilitate the development of novel solutions.