During the construction of the Mostra d'Oltremare in 1939, the thermal complex located between the ancient via Puteolis-Neapolim and a side street was discovered. Structured on several levels, fed by the Serino aqueduct and built mainly in opus vittatum and latericium, the building dates back to the first half of the 2nd century AD, although over the centuries it has undergone various interventions that have changed the organisation of its spaces. These include the entrance corridor (adapted as a cistern in the Middle Ages), some of the rooms, probably identifiable as tabernae, and the latrine, which was preceded by a small hallway with a barrel vault and the remains of an ablution basin and usually covered by a semi-dome with wall paintings, of which only a few traces remain today. The floor decoration – a black and white tessera mosaic depicting two dolphins swimming and a fantasy sea animal – is poorly preserved. The brightness was provided by the five windows in the semicircular wall. Also running alongside the perimeter of the hemicycle was a water drainage channel, continuously fed from the cistern via underground ducts, on which were perforated stone or marble seats. Originally, the entrance to the thermal building opened directly onto the vestibule, which housed a figurative black-and-white mosaic with a nereid seated on the tail of a young triton, surrounded by two cupids and dolphins, as well as traces of the plinth and the marble slab wall covering. The dressing room (apodyterion) was originally connected to the vestibule by an entrance, then later walled up. Users could opt for various routes according to their taste or therapeutic needs. The main one involved stops in four rooms heated to different temperatures, then a stop in the apsidal calidarium, with a labrum (basin) for ablutions and the basin (alveus) for hot bathing, and finally access through a passageway to the frigidarium with two basins for cold baths. Also on display here was a black-figure floor mosaic on a white background with fantastical animals, ridden or followed by anthropomorphic figures and dolphins in the corners. The partial collapse of the floors and the fall of the wall coverings have made the components related to heat production and circulation visible, such as the side ovens (praefurnia) with service compartments, the cavities below the floors (hypocausta and suspensurae) and along the walls. According to Vitruvius, these rooms are oriented southwest to optimise the use of heat and sunlight in the afternoon hours.