The church of Our Lady of Castro is situated about 5km away from Oschiri. It was built during the second half of C12th in Romanesque style on the remains on the site of an already existing church, erected by the Judge Mariano I de Lacon Gunale. This was the centre of the bishopric until 1505. Built in red trachyte, it enjoys a privileged position overlooking the vast plains of Ozieri and Lake Coghinas.

The building was originally a single nave with apse; other parts were added later.

The facade, produced with great craftsmanship in the size and squaring of the quoins, demonstrates a uncommon mastery in the coordination of the tones of the different parts, revealing that, in order to complete the work, technically experienced labourers were employed.

The facade is made up of a doorway with round arches between two pilaster strips. These divide it into three parts and, with the upper part containing a small double-vaulted bell-tower, attention is focussed upwards, thus creating greater architectural harmony.
The inlaying effect, obtained thanks to the series of blind arches along the slopes of the roof, is reinforced by a cross-shaped light which, together with another similar in the apse and three double-splayed single windows on each side of the building, serves to illuminate the stark, yet pretty interior, covered with wooden trusses. The gilt statue of the Virgin to which the church is dedicated, is also of wood. It is kept inside the church.
The external setting to this splendid country church is made up of an irregular perimeter formed of "cumbessias" and a small C17th century house for the clergy.
The Feast is celebrated every Easter Monday, when the Virgin is carried in procession to Oschiri, the celebrations continuing the whole week.