Hollowed out of the tuff, this is the most interesting cave church in the area and looks directly out onto Gravina. Preceded by a series of grottoes, which have certainly performed various functions over the course of the centuries, the church itself is built on a quadrangular plan with 5 aisles, and is supported by 14 columns in natural stone. The church contains remnants of frescoes (one depicting Christ the Pantocrator between Saint Paul and Saint Michael) and three altars with three 17th and 18th century statues, in stone and plaster, of the three archangels, as well as a medieval tomb in a niche. In a neighbouring grotto we find a series of skulls and bones, attributed, according to legend, to the martyrs of the Saracen attack of 999, but more probably belonging to corpses brought here in the course of the 17th and 18th centuries.
Located in the ancient district of Fondovico, or Fondovito, it is the place where, on 8 May every year, the celebration of the Feast of San Michele delle Grotte is held, to remember the legendary apparition of San Michele in a grotto at Monte Sant’Angelo. On this occasion the local inhabitants decorate the streets with so-called “balloni”.