Eremo di San Guglielmo, Medieval hermitage ruins in Castiglione della Pescaia, Italy.

Eremo di San Guglielmo is a ruined monastic complex whose 13th-century Romanesque church has a single nave, a semicircular apse and a barrel vault carried on two pointed arches. The facade has a round-arched portal, and only the base of the former bell tower survives on the right side.

The monastic community was founded in the 13th century by followers of Saint Guglielmo, a holy figure who embodied strict spiritual discipline. After his death in 1157, monks continued living at the site, maintaining his teachings and way of life.

This place served as a spiritual center where monks lived according to Saint Guglielmo's teachings of prayer and simple living in the wilderness. The hermitage drew followers seeking solitude and devotion away from populated areas.

The hermitage stands in woodland between Castiglione della Pescaia and the hamlet of Tirli, northwest of the town centre, and is reached on foot along forest tracks. The church and monastery are now private property and have been left to decay, so the structures are seen from outside. Wear sturdy footwear for the natural terrain.

The church façade has a round arch above the entrance lintel, and the barrel vault is carried by two pointed arches. On the right flank only the base of a bell tower remains. The monastery plan follows Benedictine models, though the site later passed to the Augustinians in 1604.