The lower section of the church dates from the early 13th century. The upper section of the church dates from the 14th century, while the cloister dates from the 15th century, although they have seen major reforms.
http://www.spain.info/en_IN/que-quieres/arte/monumentos/cantabria/iglesia_catedral_de_nuestra_senora_de_la_asuncion.html