A vast Gothic abbey church on the eastern edge of the old town, Saint-Ouen is sometimes overlooked because the cathedral overshadows it — undeservedly. The interior nave is in some ways more harmonious and less cluttered than Notre-Dame, with great clerestory windows of original 14th-century glass and a famous Cavaillé-Coll organ that draws recitalists from across Europe.
The abbey is now used mainly for concerts and ceremonies. The garden behind, beside the modern Hôtel de Ville, is one of the few open green spaces in the old town and a pleasant lunch spot.