The Museum of Sacred Art in Campiglia Marittima is located in the rooms underneath the Church of San Lorenzo and conserves liturgical furnishing from the Propositura in Campiglia: silverware, chalices, monstrances, pyxides, reliquaries, vestments, statues, paintings and memorial stones dating to between the 16th and 19th centuries.
Works in the museum include a bronze Christ attributed to Antonio Susini from the end of the 1500s, an ophitic column from the 1700s, a 14th-century bell and a 1652 Ecce Homo by the Florentine painter Alessandro Frigoni. There is also a large collection of reliquaries, among which there is a small temple that houses the relic known as the "Milk of the Madonna", dating back to the end of the 16th century.