Alghero's cathedral was begun in 1530 in the late Catalan Gothic style. Construction ran on for two centuries, so the building is something of a stylistic patchwork — Gothic ribbed vaulting at the apse end, a Renaissance nave, a Baroque dome, and an octagonal bell tower that is one of the few intact Catalan Gothic structures left on the island. The exterior is rough trachyte stone, austere from the outside.
The five-sided apse, accessed through a side chapel, is the highlight: a five-petalled space with the original 16th-century vaulting and choir stalls. The bell tower is open to visitors in summer; climbing it is the easiest way to get a view back down over the red-tiled roofs of the old town and out across the bay. Free entry to the church; small fee for the tower.