The thermal complex of Sant Grau is one of the best-preserved Roman buildings in the province of Girona. Built in around 50 AD over the remains of previous thermal baths dating from the 2nd century BC, it is composed of a large central swimming pool with steps, surrounded by an arcaded corridor, and three wings of rooms. The main entrance, reception and changing rooms were located at the south end of the building, while two possible saunas or massage rooms were located at the east end, along with a sacred space (with the remains of an altar) where the thermal water that filled the swimming pool flowed in. The remains of the drainage conduits are preserved on the south-west side. This system ensured the constant renewal of the water, preserving its temperature and cleanliness and preventing the build-up of calcareous deposits.

Following a series of alterations, in the Middle Ages the thermal baths were incorporated within the complex of Caldes Castle, of which a wall and three towers are preserved right next to the Roman building. The baths remained in use until the 19th century, since the building was converted into a hospital. The complex has recently been restored and turned into a museum, and the interior can now be visited (by appointment).