Castirla is a mountain municipality which covers an area of 24.32 km2, from the Agatu (1641 m) and Pinerole (1951 m) mountains to Golo. It belongs to the Talcini microregion.

The village of Castirla is layered on a mountainside at about 450 meters above sea level, grouped around the parish church of the Annunciation, dating from the 18th century.

Below, the cemetery shelters the Romanesque chapel of Saint Michel, dating back to the 12th century, classified as historic building since 1958. In Castirla, a 15th-century Genoese bridge with three arches crosses the Golo. This bridge is nicknamed the "Devil's Bridge, because according to the legend it was built overnight by the devil.