The cathedral of the Sierra Monument · Villacastín, Comunidad de Ciudad y Tierra de Segovia, Segovia Image of Villacastín, not of the place itself. The church of San Sebastián was begun in 1529 with the revenues of the Mesta and completed in the seventeenth century: a hall plan of three naves of similar height, star ribbed vaults and the funerary chapel of the Mexía family. It was declared a Monumento Nacional (Spain's heritage designation in force until 1931) in 1944. Photo: Villacastin (CC BY-SA 3.0) What to see and do in Villacastín