Before the main-entrance, there was a small apartment, which must have served as a pronaos. In it was a mosaic of Silvanus (see infra) and an altar (now lost). In the middle of the apartment the remnants of a 'chimney' ('cammino') were found, probably behind an altar. On entering the sanctuary, one notices a peculiar altar.
The Mithraeum itself (L. 16.70 Br. 5.