Stands on the left bank of the Upper Cesano Valley on the south-western border of the Province of Pesaro, below the wooded eastern slopes of Monte Catria (1702 m).
The castle was founded in the 13th Century by the free commune of Gubbio because of its strategic position in defending and controlling one of the routes across the Apennine mountains. From 1384 it became part of the lands of the future Duchy of Urbino. In 1481, Duke Federico da Montefeltro commissioned Francesco di Giorgio Martini to build an imposing castle. Unfortunately nothing remains except for a detailed description given by the architect in his well known Treatise on Architecture. Despite the loss of the castle, the town still preserves the layout of a typical medieval fortified town, with two of the original entrance gates, the Porta Santa (with clock tower above it) and the Porta Macione (13th Century). Still older is the early Christian crypt of San Biagio (7th or 8th Century) built using materials from a pagan temple dating back to the Roman period. The crypt stands just outside the town in the present cemetery. Also worthy of note is the shrine to the "Santa Maria della Canale", decorated with a 15th Century fresco. An agricultural association still exists in Serra Sant'Abbondio which is a direct descendent of the medieval "Università degli Uomini Originari", a guild to which the original male inhabitants of the town belonged.
The famous Camaldolensian hermitage of Santa Croce di Fonte Avellana stands 7 km away from the town, among woods of larch, oak and hazel ('avellana'), overshadowed by the peak of Monte Catria. It was founded in 977 and remembered by Dante, who stayed here in 1310, in his Divine Comedy. The imposing medieval complex, as well as the church and crypt, has a chapter house, cloister and magnificent scriptorium.