Mixed Reality has emerged as a valuable tool for the promotion of cultural heritage. In this context, in particular, the metaphor of virtual portals allows the virtual visit of monuments that are inaccessible or no longer exist in their original form, integrating them into the real environment. This paper presents the development of a Mixed Reality mobile application that proposes a virtual reconstruction of the church of Sant’Elia in Ruggiano, in the southern province of Lecce (Italy). By placing the virtual portal in the same place where the entrance of the church was located, the user can cross this threshold to enter inside and make a virtual journey into the past. The user experience was evaluated by administering a questionnaire to 60 users who tried the application. From the data collected, four user experience factors were identified (interest, focus of attention, presence and usability), which were compared between young and old, male and female users, and between users who had already visited the church in person and all other users. In general, the scores reveal a total independence of the other three factors from usability and a very high level of interest.