The patron saint of Castelpetroso is Saint Martin of Tours, celebrated on 11 November. The parish church dedicated to him dates from the second half of the 13th century and underwent Baroque influences in the 17th century: it has a rectangular single-nave plan, with a turreted bell tower, and holds a mosaic depicting the saint, a painting probably from the 17th century, and several works by the Molise master Amedeo Trivisonno.
The town, however, is best known for the basilica-sanctuary of Our Lady of Sorrows, dedicated to the patroness of Molise. According to the testimony of two shepherd girls named Serafina and Bibiana, the Virgin first appeared to them on 22 March 1888 at Cesa tra Santi, on the slopes of Monte Patalecchia; further apparitions followed, and the phenomenon was later recognised by the Church. Among the territory's other religious buildings is also the church of the Madonna della Libera, in the hamlet of Indiprete, which according to local tradition originates from a miraculous event linked to a painting of the Madonna.
