The church has a basilica plan with three naves, of which the center is slightly wider. The ships are finished off in semicircular apses, one of them left, it is slightly offset by a subsequent reform. In the south facade rises a circular tower, and next to it, the main entrance on a ledge of the wall. This entry is perhaps one of the most famous images of the art of Cantabria. The door is half point with five simple archivolts supported by columns with capitals, today very deteriorated day. On the door is a frieze with Pantocrátor held by four angels and six figures on each side. The entrance is topped with a pediment with sculpture of Santa Juliana. This whole area is modified to have been restored in the seventeenth century. In the late twelfth and early thirteenth protogótico style reforms, such as the vaults of warheads sections of ships, ships with cruciform pillars with half-columns and dome there on the cruise they are made. The cloister is attached to the ship of the Gospel and it seems that was built in the late twelfth century. The arches of the three oldest crujías are, for the most part, although some midpoint is already targeted. This side arcades are however pointed, Cistercian tradition and made in the fifteenth century. It is important capitals collection with a wide iconographic repertoire ranging from plant types and tracery up the narrative theme. In addition, in different parts of the collegiate church there are reliefs of protogótico style Pantocrator still retains some of the original color, a virgin with child, Santa Juliana and four apostles. Other objects of artistic interest are the Romanesque baptismal font, decorated with the scene of Daniel in the lions, the tops of the graves preserved in the cloister, two Gothic virgins found in the sacristy, two Gothic saints rough size and exceptional processional cross from the early sixteenth century.