The Baths of Mithras (excavated in 1939-1940) were built in the Hadrianic period (opus latericium) and modified in the first quarter of the fourth century (opus latericium and vittatum). To the east of the building was an arcade of eleven arches, that later became part of the baths. The main entrance to the building is on the east side and leads to room H, an apodyterium or vestibule. Behind that are large halls (F-G), the function of which is unknown. Room E, with niches and a basin in the west part, was a frigidarium. Here a mosaic of Ulysses and the Sirens was found. To the east is a small basin (I). Room D was a tepidarium, room B a sudatorium, later extended with an apse containing a basin. The southernmost room (A) was a caldarium, with two rectangular basins (a later addition). The building was decorated with two imagines clipeatae, shields with portraits. The portraits were made c. 100 AD and probably depict members of the family that had financed the baths.

The underground service area is preserved very well. In the south part of the ground floor of the building (to the south of room A) is a narrow corridor, to the south of which is a room for a waterwheel. Wear-marks are visible on the side walls. The wheel had a diameter of 7.25. It was operated by a slave and lifted ground water to a cistern. The output was 1000 litres per hour (a basin in the caldarium held 1500 litres). Later a second wheel was added at a higher level: water was raised to the top floor of the baths. Also in the underground area a statue of Vulcanus was found in a niche, apparently a fountain, in which the statue clearly does not belong.

In the north part of the building (room G) is a staircase leading to the service area. Here a mithraeum was installed (opus vittatum) in the late second or early third century. The cult statue of Mithras, about to kill the bull, was found in situ, and a plaster cast has been placed in the shrine. Light falls on the statue in a dramatic way, through an opening in the ceiling, as it did in antiquity. In the north-east part of the service area is a tiny fullery.

In late antiquity the building was no longer heated: tubuli were taken from the walls and furnaces were filled in. The basins of the caldarium were filled with cold water. The various basins and fountains may now have been used for baptizing: a Christian oratory was installed in room G.