Crypte Archéologique de l'İle de la Cité

The Crypte Archéologique de l'Île de la Cité lies beneath the open square in front of Notre-Dame Cathedral. It is a sprawling, subterranean site that houses the physical foundations of Paris, preserved exactly where they were uncovered. You can identify the entrance by its location on the Parvis Notre-Dame, tucked away beneath the level of the modern street.