The church has one nave and preserves in pure Romanesque style the triumphal arch, chancel, apse and part of the walls.

The roof of the nave is Gothic and was later made probably because of a collapse of the original.

The triumphal arch leads to the presbytery covered by a barrel vault.

Following a second arch starting from prismatic corbels leads to the oven vaulted apse.

All apsidal area highlights for its harmony and the richness and variety of its decoration.

All that makes this temple one of the most visited of Cantabria.

Sources: 

García Guinea.-Románico en Cantabria-Guías Estudio

http://canales.eldiariomontanes.es/patrimonio/bics/bic16.htm

http://www.arteguias.com/catedral/colegiatacervatos.htm

http://www.cantabriarural.com/esp/turismo-rural-cantabria/informacion-anadida/lugares-de-interes/colegiata-de-san-pedro-en-cervatos/606-4-146-33-esp.html