Catalonia: Tarragona – Cathedral of Tarragona
Originally, this was a Roman temple, then early Christian church, then a Moorish mosque, and finally a Romanesque cathedral and finally a gothic cathedral, this is a smorgasbord of styles both inside and out. Interior has multiple naves laid out as a cross joint in an octagonal dome and there are many small and large chapels around as well as a courtyard and tombs and cloisters. Your neck will hurt staring up at all the sumptuous decorations, statues, paintings, and vaulted ceilings.