Basilica of St Denis, Paris, France (Basilique Royale de Saint-Denis). Home to the tombs of the French monarchy and the building which marks the transition from Romanesque to Gothic architecture. Without doubt worth the metro ride from the centre of town.
The Basilica of Saint Denis. This amazing tomb is probably one of the most splendid and impressive ever created and it is a miracle that it survived the violence of the revolutionary era, when the royal tombs at the Basilica of St Denis were desecrated and destroyed and their contents thrown into a common grave.