Ste-Onenne, Parish church in Tréhorenteuc, France.

Ste-Onenne is a low parish church built of rough brown and grey stone, with a steep slate roof and a slender slate spire topped by a cross. Its walls include a round window with a stone ring and a pointed-arch window with tracery. Inside, the boat-hull-shaped wooden vault and benches were made by cabinetmaker Peter Wissdorf, a German prisoner of war, in 1945.

A Christian oratory existed at Tréhorenteuc from the 7th century, and a priory was founded in 1191. Anne of Brittany took the parish under her protection by a mandate of 27 October 1489 and gave a banner of Saint Onenne in 1506. The parish church was rebuilt in 1516 by Dom Hamon, then restored by Abbé Gillard between 1942 and 1962.

The church is nicknamed the Church of the Grail. Between 1942 and 1962 Abbé Henri Gillard commissioned fittings that mix Arthurian legend with Christian themes: the first stained-glass window, the Round Table, was made by Henri Uzureau in 1943. The Stations of the Cross include the village houses, Gillard himself and two German prisoners of war.

The church stands in Tréhorenteuc, within the Brocéliande forest area associated with Arthurian legend. A monument to Abbé Gillard, who led the reconstruction from 1942 to 1962, stands in front of the building. The village lies in a remote part of inland Brittany, reached by road; the church is the parish church of the commune.

The church is nicknamed the Church of the Grail, and its Stations of the Cross include portraits of Abbé Gillard himself and two German prisoners who helped him in 1945. The stations run from north to south rather than in the usual order.