## 1 Introduction  
Cultural heritage faces many threats to its security, both environmental, such as pollution and climate change, and man-made, such as the intentional destruction of cultural heritage. In this scenario, technology gives us unprecedented opportunities to preserve and protect it. Digital technologies, from 3D simulation to artificial intelligence and virtual/augmented reality, are being used to ensure cultural heritage preservation. Among the tasks accomplished during the conservation of cultural heritage, restoration stands out. In particular, virtual restoration, a type of restoration, obtains images of the original state of a building by analyzing its ruins or a fragment of the building. These virtual restorations were carried out using the techniques of representation and planimetric restitution of the time, such as painting, engravings, and models. In all cases, the starting point was a theoretical assumption of the original state. This assumption was based on the buildings that maintained part of their integrity, on drawings and engravings from other periods, and even on texts and manuscripts that described the structure under study with greater or lesser fidelity [1]. Virtual restoration of historic buildings is a powerful tool for transferring knowledge to society. By combining advanced technology with the richness of cultural heritage,new possibilities open for (a) education, (b) preservation, and (c) cultural promotion. These practices not only help keep the past alive but also enhance our understanding and appreciation of the cultural legacy we have inherited. In the field of education, these tools improve (i) accessibility to cultural content, allowing people from all over the world and of all backgrounds to access and explore historic buildings without the need to travel or create complex infrastructure to accommodate the sites. Additionally, the (ii) interactivity of these interventions can offer contextual historical, aesthetic-artistic, and architectural information. Finally, (iii) immersion in virtual reality (VR) and augmented reality (AR) environments provides experiences that can be more effective than traditional methods. Regarding heritage preservation, virtual restoration serves as a (i) detailed record of the current state of the building and allows for monitoring the lifespan of its construction elements, enabling the identification of parts at risk of deterioration to implement appropriate preventive measures. The virtual restoration models also offer significant possibilities to be used as (ii) references in physical restoration projects, providing very precise information about the original state. In terms of cultural promotion, virtual restorations can enhance (i) the attraction of cultural tourism to many regions, especially rural ones, in an innovative way and without the need for large investments in museum infrastructure. Moreover, mobile applications and AR-based tourism guides can provide (ii) personalized and enriched experiences for all types of visitors. Artificial intelligence (AI) could play an important role in heritage preservation, not only for its use in the study of physical remains but also for its application in virtual restoration. Among all AI techniques, deep learning (DL) models have stood out for obtaining very good results in the field. DL was defined by [2] as those models that can learn the representation of a dataset using different levels of abstraction. Image restoration is linked to the virtual restoration of cultural heritage, which, in the case of DL models, can be framed as image-to-image translation. Image-to-image translation is a method that uses data to translate the possible representation of a scene to another representation, usually by super-resolution, colorization, and inpainting. In [3], the aim of the latter is described as starting from a region of missing pixels, generating those that are realistic and semantically coherent with the existing ones.