Monastery of San Guillermo de Peñacorada Monument · Cistierna, La Montaña de Riaño, León Remains of the medieval monastery at the foot of the Peñacorada massif, in the municipality of Cistierna (León), founded in the 11th century as one of many monastic houses through which the lay aristocracy controlled the sacred sites of the Kingdom of León. It is documented from that century as Santa María de los Valles; it was not until 1289 that Sancho IV gave it the name San Guillermo and placed it under the authority of the monastery of Sahagún. Today barely any remains survive, due to neglect and plunder, although an excavation in 1915 found in the presbytery bones attributed to a hermit identified with the saint, greatly venerated in Cistierna: in a cave on the outskirts his image rests, to which every 28 May a pilgrimage climbs up to the hermitage built on the same spot. Photo: Emracosta (CC BY-SA 4.0) What to see and do in Cistierna