This monastery belongs to the Cistercian order and was founded by the knight Ero de Armenteira in 1168. It has a square cloister, a kitchen, and a tower, all in the 18th-century Baroque style. The monastery was abandoned after the sale of church lands in 1835. The church has a floor plan in the shape of a Latin cross, three naves and three semicircular apses. The central nave is crowned with a pointed barrel vault, and the side naves with groin vaults. The transept has a vault raised on Mudéjar-style pedentives. On the façade, the 12th-century rose window is of particular interest. The whole complex has today been rebuilt thanks to the Association of Friends of the Monastery of Armenteira.