The thermal bath areas that can be accessed from the passage area of the biapsidal hall 
start from the frigidarium, a space dedicated to cold baths, with an octagonal plan
around which is arranged a
Corinthian order
colonnade that would have supported the
trabeation
and a dome, probably with an opening in the centre, which let in rainwater.
All the walls of the frigidarium were lined with
marble crustae
, which also denoted its public use.
The healing and invigorating baths took place in the two swimming pools to the north and south used for swimming and immersion respectively.
The elegance of the thermal bath environment is shown not only in the rich architectural structure and coverings, but also in the mosaics that adorn the floor of the octagon, enlivened by a brightly coloured marine thiasos with mermen, nereids and fisherman erotes.
The fantastic mythological scene is enclosed by six
apsidal niches
with realistic themed depictions of mutatio vestis, or changing of clothes.
