The Cathedral of St. Peter, like the Cathedral of St. George, is also on the UNESCO World Heritage list. After the earthquake of 1693, the church was restored, and it now has a very elegant front, embellished by four statues, which represent San Cataldo, Santa Rosalia, St. Peter and the Madonna, which enrich the second order, the apex at the front is topped by a sculpture, in high relief, of Jesus Christ in triumph. A monumental flight of steps adorned with statues of the 12 apostles on the sides makes the entrance even more majestic. The interior, on the other hand, has three naves with 14 columns supporting Corinthian capitals, a beautiful floor from 1871, inlaid with white, coloured and pitch black marble. The once sumptuous, rich frescoes depict scenes from the Old and New Testament, and were started in 1760 by the local painter Gian Battista Ragazzi with the help of his son Stefano, and were completed around 1780, but probably only by the son.

The right aisle contains two groups of statues: a replica of the "Madonna of Trapani" by Francesco Laurana, attributed to Giovanni Pisano (uncertain attribution), and the polychrome "Saint Peter and the paralytic," by Benedetto Civiletti from Palermo, in 1893. The 'monumental organ, built by the Polizzi brothers and inaugurated in 1924, is composed of 3200 reeds, 32 registers and two keyboards.