The Diocesan Museum of the cathedral houses the archaeological finds and the works of art coming from the diocesan territory, dating from the II century to the XX century, arranged on three floors and divided in four sections, such as for example finds coming from the catacombs of Santa Mustiola and Santa Caterina; fragments of a ciborium coming from disappearance basilica of Santa Mustiola; two reliquary casket (XV century) in wood and ivory, made by the workshop of Embriachi; 21 illuminated manuscripts (XV century), coming from the Abbey of Monte Oliveto Maggiore, decorated by painters like Sano di Pietro, Francesco di Giorgio Martini and Liberale da Verona, commissioned in 1456 by Francesco of the railing, Abbot General of the Olivetan Order. The path continues with the visit of the so-called labyrinth of Porsenna: this is a series of underground tunnels Etruscans (V century b.C.), which largely wind under the dome, connected with the surface through wells, subsequently buried. The name of the labyrinth derives from the description of Pliny the elder of the mausoleum of Porsenna, the legendary Tomb of the Etruscan King protected, according to historians Latini, by a labyrinth. Most probably this is the water supply system, dug by the Etruscans in the archaic era. The system is particularly vast and ingenious, dug in ductile sandstone, to a maximum depth of 25 meters. The system is composed of a dense network of passageways, wide on average one meter tall and from two to five meters, sometimes reinforced from blocks of stone. There are encountered tanks and small basins to collect the water, both through infiltration, which with flaps. The labyrinth leads up to a great reservoir Etruscan-Roman (I century a.C.) and the ascent on the Bell Tower (XII century) 24 meters of height. From the museum starts the visit to the catacombs of Santa Mustiola, for the smaller Santa Caterina d'Alessandria and the Paleochristian cathedral (VI century).