The Cathedral of Saint-Pierre-et-Saint-Paul is one of the great Gothic churches of France, and one of the least visited. Construction stretched from the 13th to the 17th century, which means the nave shows the full evolution of Gothic style — from the powerful early choir to the elegantly late Flamboyant west facade. What sets it apart from better-known cathedrals is the glass: around 1,800 square metres of medieval stained glass, more than any other church in France. The north rose window alone, from the 13th century, is worth a long look.
The glass ranges from deep 13th-century blues and reds to the more luminous Renaissance panels in the nave chapels. Come on a bright morning when the light is moving through the apse, and the interior becomes extraordinary. Entrance is free. Allow at least an hour — more if you are serious about the glass.