The entrance lies in 2, Via Portica and leads to the crypt of the demolished church of S. Nicolò, where the museum exhibits Umbrian and Roman remains, mostly tombstones, cinerary urns and inscriptions.

It conserves as well the wall which delimited the large terrace on which has been built the Temple of Minerva rising in Piazza del Comune and the calcareous slabs of the Roman street pavement.

A cuniculus leads underneath the Piazza del Comune, to the so-called Forum Romanum (which on the contrary was located at the actual church-square of the Cathedral of S. Rufino) and to the stairs that lead from a large terrace of 85 x 45 m to the podium of the temple.

Opposite to the front of the temple has been discovered the podium of a tetrastylos which according to an inscription contained a sculpture group of Castor and Pollux. A similar situation is to be found in Rome, at the Palatine hill, in front of the temple of Apollo