A red-brick church from the 11-12th Century, it may well be the largest Romanesque construction in the world - perhaps because it was an important stopover on the pilgrimage to Santiago. Huge as it is, it's the only remaining part of the former Abbey of Saint-Sernin. Notable features are the great bell-tower, the gates, the "ambulatory" passage, and the thunderous organ. In the 19th C the church was "restored" by the famous French architect Viollet-le-Duc: some of his re-imaginings of the Middle Ages are now being undone.