The centrepiece of the Cidade Velha, the sé was completed in 1251 but heavily damaged in the 1755 earthquake. What you see now is a variety of Renaissance, Gothic and baroque features. Climb the tower for lovely views across the walled town and estuary islands. The cathedral also houses the Museu Capitular, with an assortment of chalices, priestly vestments and grisly relics (including both forearms of St Boniface), and a small 18th-century shrine built of bones.
The blocky, castle-like cathedral occupies what was probably the site of a Roman temple, then a Visigoth cathedral and then a Moorish mosque. Only the tower gate and several chapels remain of the original Romanesque-Gothic exterior – the rest was obliterated in 1755. The interior has very elaborate baroque side altarpieces, and the altar itself is flanked by matching vaulted Gothic chapels. The baroque organ is worth noting.