Castelluccio is a village in Umbria, in the Apennine Mountains of central Italy. Administratively, it is a frazione of the ca. 28 km distant town Norcia. According to the 2001 census, it had close to 150 inhabitants.
The village lies at 1452 m, making it the highest settlement in the Apennines. It lies above the "Great Plain" (Piano Grande - 1270 m), next to the Monti Sibillini National Park.
Rain and meltwater accumulate on the surface of the plain, which is made of largely impermeable sediments. The greenish ditches drain the water towards openings called Ponors, which are part of the karstic underground drainage system. If the karst drainage is blocked for any reason, water backs up and turns the plain into a temporary lake.