The Catedral Nueva's largely Romanesque predecessor, the Catedral Vieja is adorned with an exquisite 15th-century altarpiece, one of the finest outside Italy. Its 53 panels depict scenes from the lives of Christ and Mary and are topped by a haunting representation of the Final Judgement. The cloister was largely ruined in an earthquake in 1755, but the Capilla de Anaya houses an extravagant alabaster sepulchre and one of Europe's oldest organs, a Mudéjar work of art from the 16th century.

The cathedral was begun in 1120 and remains something of a hybrid: there are Gothic elements, while the unusual ribbed cupola, the Torre del Gallo, reflects a Byzantine influence.