The Parish Church of St Mary, in Tanes, is on the edge of Tanes Reservoir and consists of a central body, the nave and various additions that form a curious ensemble of rare proportions in Asturian churches.
The central body comprises the rectangular nave and straight apse, taller than the rest of the structures. Inside, the nave is divided into three bays by pilasters with adjoining columns and transversal ribs. It is covered with groin vaulting.
The chancel in the east end opens onto a small sacristy covered with groin vaulting. At the west end of the nave, there is a wooden choir supported by a triple stone archway. To the left of the nave is the Chapel of the Nazarene, the oldest building in the ensemble. This chapel is a square enclosure covered with a barrel vault.
The western and southern façades are protected by a porch, closed at the front and opened by arches on the south side.
The porch leads to a square enclosure that served as a schoolhouse and teacher's residence.
The new sacristy is found in the southwestern corner of the façade. It is a rectangular enclosure and has its own façade.
