Its name comes from the apparition of the Virgin inside the trunk of a walnut tree. Thirteen villages of the Sobrarbe come to this sanctuary in pilgrimage. Although its origins appear to be Romanesque, the majority of the construction is from the 16th to the 18th century.
The sanctuary is formed by an amalgamation of constructions from different eras including the church, several “casales” or pilgrimage chambers (where the attending villages met and the rooms were named after the revered saints), stables, a cellar and a cemetery. The collection has an unusual design centered around a courtyard, which is accessible by a vestibule.
The church has a longitudinal layout, with a nave covered by a barrel vault. It also has a straight chevet covered by a dome over pendentives. The decoration is of popular baroque style. The Coronation of the Virgin appears in the keystone of the arch and the the four evangelists appear on the dome.
The exterior door opens underneath a semicircular arch, in which the keystone features an engraved cross of Lorena, dated 1552. Some windows are decorated with high relief images of faces and decorative wreath designs on the windowsills.
