UNESCO World Heritage Site. Believed to be built upon a hermitage where St. Emilian lived. The monastery is abandoned now.
Wikipedia https://it.wikipedia.org/wiki/Monastero_di_San_Millán_de_Suso
UNESCO Website http://whc.unesco.org/en/list/805
Address Carretera del Monasterio de Suso, 26226 San Millán de la Cogolla, Spain
Coordinates 42°19'45.763" N -2°52'21.783" E