La Crypte Archéologique
Time Out says
Hidden under the forecourt in front of the cathedral is a large void that contains bits and pieces of Roman quaysides, ramparts and hypocausts, medieval cellars, shops and pavements, the foundations of the Eglise Ste-Geneviève-des-Ardens (the church where Geneviève's remains were stored during the Norman invasions), an 18th-century foundling hospital and a 19th-century sewer, all excavated since the 1960s. It's not always easy to work out exactly which wall, column or staircase is which - but you do get a vivid sense of the layers of history piled one atop another during 16 centuries.
7 place Jean-Paul II
|Price:||€4; €2-€3 reductions; free under-14s. PMP|
|Opening hours:||10am-6pm Tue-Sun|