In 1926, during an excavation carried close to an XVIII century church in a small town in Lugo (Spain), the Roman Temple of Santa Eulalia de Bóveda was discovered by chance. Built in the IV century, it is made up of a single room, with a vault 6 m wide and 9 m long, which protects the pool that occupies the space almost entirely. Possibly, in its beginnings, the temple was intended for some type of cult or healing activity related to baths, since the walls had bas-reliefs and paintings that show different interventions of this type and, above all, an ingenious work of hydraulic engineering, which it guaranteed good hygienic and health conditions in the pool. In fact, the water was crystal clear when the monument was discovered. Precisely for these unique paintings, dated to the VII century, the authorities have carried out different actions to try to dry out and drainage the building, in order to preserve these coatings of great historical and heritage value. Unfortunately, however, these actions only served to further aggravate the already existing problems. This paper describes the temple, as well as the actions that have been carried out so far to stop its decay, the last tests and survey developed during year 2022–2023 to understand how this complex building really works, such as salt analysis, continuous measurement of climatic conditions, moisture content in the masonry, hygrothermal conditions inside and outside the temple, smoke tests to study air movement, etc., and the information that is considered should be taken into account to design the proper intervention that would guarantee the durability of one of the most unknown, mysterious and best preserved monuments from the Roman era in Spain.