The Church of St Peter the Apostle in Grotte di Castro was built towards the end of the 11th century and has undergone various alterations and architectural transformations over the centuries. Today, the building features a simple single-nave structure, though it is enriched by numerous works of art of great interest.

Inside, there is a 16th-century statue of the Assumption of the Virgin Mary, flanked by two paintings created in the late 19th century by Luigi Fontana: Saint Peter Healing the Cripple and Saint Paul Preaching in Athens. Also particularly striking is the canvas depicting Salome witnessing the beheading of Saint John the Baptist, attributed to the 17th-century Roman school.

Other notable features include an 18th-century crucifix and the tomb of Cardinal Carlo Salotti, created in 1948 by the engineer Luigi Fracassini and the sculptor Romeo Cordelli. More recent is the painting entitled The Mission of the Apostles, painted in 1956 by Father Nazareno Confaloni.