Viterbo's historic center is one of the best preserved medieval towns of central Italy. Many of the older buildings (particularly churches) are built on top of ancient ruins, recognizable by their large stones, 50 centimeters to a side.

The main attraction of Viterbo is the Palazzo dei Papi, that served as a country residence and a repair in time of trouble in Rome. Begun as the Episcopal Palace in 1255, from 1257 on, with the arrival of Alexander IV the works were hurried and were completed in 1267 with the construction of the famous loggia, which in origin was a double one, but then the northern part collapsed under the excessive weight and has not been rebuilt ever since. The columns of the palace are spolia from a Roman temple. At the right of the Loggia begins the proper Episcopal Palace with the Sala Gualtiero(Throne Hall), the Gallery, the Library Hall, the Hall of Arms and the Appartment of the Cardinal.

The second most important monument of the city is the Cathedral of S. Lorenzo. It was erected in Romanesque style by Lombard architects over a temple of Hercules. It was variously rebuilt from the sixteenth century on, and was heavily damaged in 1944 by Allied bombs. The notable Gothic belfry is from the first half of the fourteenth century, and shows influence of Senese artists. The church houses the sarcophagus of Pope John XXI and the picture Christ Blessing by Gerolamo da Cremona (1472).

Built originally in Romanesque forms, it has been modified in the subsequent centuries. The actual front dates back to 1570, while the Gothic -Tuscan campanile with its four rows of double double-windows dates back to 1368. The three-aisled interior with the columns with magnificent capitals and the finely decorated beamed ceiling is very airy. In the nave you find the rests of a Cosmatesque pavement. In the right aisle there is a marble font of 1470 by Maestro Francesco di Ancona. In the apse of the left aisle, you find a painting of Byzantine school of approx. 1195 representing the Madonna della Carbonara, taken from the homonymous Mother Church of the Knights of the Order of Saint-John-of-Jerusalem, and remains of frescoes of 1290. Past the entrance to the Baroque furnished sacristy, there is a painting ascribed to the Mantegna("Il Salvatore", 1472) and towards the exit, remains of 14th century frescoes and the tomb of John XXI, died tragically in Viterbo in 1277 and mentioned by Dante in his Paradise. John XXI has been by the way the only Portuguese Pope in history.

The Museo Civico (City Museum) houses many archeological specimens from the pre-historical to Roman times, plus a Pinacoteca (gallery) with paintings of Sebastiano del Piombo, Antoniazzo Romano, Salvator Rosa, Antiveduto Grammatica and others.

Rocca Albornoz, also called Rocca del Papa, greatly destroyed by the bombings in 1944 and since then renovated, the imposing building had been erected by Cardinal Albornoz, who died in Viterbo in 1367. The Rocca Albornoz houses the Museo Nazionale and a great permanent exhibition on the Etruscan and domestic architecture.

The Chiesa di San Giovanni Evangelista in Zoccoli was built in the 11th century, because of the poverty of the parish, it has not been modified substantially. The front which leans on two perpendicular arches, is rather characteristic. It has a 16th century portal with a painted lunette and a beautiful rose-window. In the interior, there are various frescoes and a precious polyptych of 1441 by the Viterbese painter Francesco d'Antonio, called the Balletta.