Functioning more as a museum than a house of worship, the old cathedral is a squat Romanesque structure begun in 1140, and its sight lines to the altar are obscured by the sheer bulk of its interior supports. Nonetheless, it retains some powerful religious art, most notably the mid-15th-century altarpiece of 53 compartmentalized scenes painted by Nicholas of Florence to delineate the life of Christ and scenes of the Virgin Mary. It is not uncommon to see pilgrims entranced by the masterpiece, spending hours on their knees in prayer in the medieval gloom as they contemplate each scene. After viewing the church, stroll through the enclosed cloisters. Two chapels are of particular note: the Capilla de San Martín with frescoes painted in 1242, and the Capilla de Santa Catalina, replete with gargoyles.