The seventeenth-century town (a fine example of Baroque town-planning), accessed by two gates, is dominated by the abbey church and the Palazzo Doria Pamphili. The church is a spectacular example of an ancient abbey, built by the Cistercians of Pontigny in the early thirteenth century. The facade, surrounded by two seventeenth-century bell towers (designed by Borromini), surmounted by pyramidal spires, has a large Gothic mullioned window. The external part of the polygonal-shaped apse with a double order of single-light windows is worthy of note.

The solemn Latin-cross interior with cross-vaults and a nave and two aisles divided by pointed arches supported, alternately, by cruciform pillars and columns, recalls the Burgundian style, and is one of the most extraordinary examples of Gothic art in the Viterbo area. The coat of arms on the capital of the first column on the right in the nave towards the altar (the oldest and rarest piece of evidence of the original construction) is that of Cardinal Francesco Todeschini Piccolomini.

The right-hand transept preserves an excellent standard by Mattia Preti (1613-1699) depicting St.Martin on horseback in the act of giving his cloak to a poor man (on the back, Christ in Pietà). The lefthand transept contains an organ (early twentieth century), which works by means of mechanical transmission, that came from an Anglican church. Inside the Baroque railing with the Pamphili insignia (beginning of the right-hand ais1e) there is a baptismal font of the seventeenth century.

On the floor of the nave, a large marble plaque, dictated in the seventeenth century by Princess Olimpia Maidalchini, recalls Cardinal Raniero Capocci, benefactor of the building, and Cardinal Francesco Piccolomini, the commissioner of the substantial alterations to the abbey in the fifteenth century. In the presbytery there is another marble plaque on the tomb of Princess Olimpia, who at some time in the mid-seventeenth century was responsible for the construction of the Palazzo on various abbey buildings and the restoration of the chapter-house that opens onto the site the abbey cloister once occupied. The projects also involved the new city layout of the town, with one of the first examples of small terraced council houses.

The Palazzo, completely rebuilt in the 1980s by the Provincial Tourist Board of Viterbo of that period, now houses a congress and cultural centre.