The monastic church of Santa María in Oia, the current parish church, dates back to the late 12th century and early 13th century. It is characterised by the absence of decorative elements, typical of austerity of the Order of Cistercians.   The temple has a Latin cross floor plan, with three naves forming a T and a smaller nave that forms the cross. The central nave is the tallest and is covered by pointed barrel vaults. It ends in the central chapel.   In the 16th century, the choir and the sacristy were built, with singular flat vaults and curvy ribs, done by Bartolomé de Hermosilla. Above the chevet’s entrance arch there are some paintings representing the king Alfonso VII and his son Sancho, as well as some coats of arms of military orders.   The current facade dates from the 18th century and is formed by two bodies: the lower one has in the centre a simple portal with a niche for the Virgin Mary’s image, while the upper body has a triangular pediment finished with the coat of arms of the monastery. From the 18th century also remains the Baroque tower built over the sacristy to replace the old bell tower.