The building, located between the thermal bath n. 1 and the castellum aquae (a water cistern fed by an aqueduct and in turn feeding a network of distribution pipes), was discovered in the fifties and has only been partially excavated; its cemented vaults collapsed but are still preserved in the building. Only a few rooms of the structure have been released; they were built in opus vittatum mixtum (alternating rows of bricks with blocks of stone cemented with lime). The western side of the building retains traces of a coating of white plaster painted with stripes of various colors.