There is an authentic Roman mosaic underneath the High Altar. ITT Museo della Cattedrale Piazza del Duomo. .Q (0578) 22 64 90. Open daily. Adm charge 0 partial. The museum, found in the cloister of the cathedral, has a display of Roman, Lombardic and medieval sculpture. In this museum, visits can be arranged to the underground galleries beneath the city, dug by the Etruscans and used as catacombs by early Christians in the 3rd-5th centuries. Santâ€™Antimo Â© Road map D4.