alrighty then
The Crypte Archéologique de Notre-Dame
Beneath the streets of central Paris, the Crypte Archéologique is a huge and haunting space extending 80m under the shadow of Notre Dame Cathedral and an intriguing attraction for any visit to Paris.
The Crypte Archéologique de Notre-Dame is an atmospheric time capsule which explores the lives and artifacts of the tribes and civilizations that dwelt in Paris long ago. Here are located the telling remains of a house from Lutèce, the precursor to Paris. There are numerous Gallo-Roman artifacts, which provide a fascinating insight into the lives of the mighty Roman Empire and how they lived in Paris.
This fascinating attraction includes a splendidly recreated settlement of the Parisii, the Celtic tribe that first settled on the site of Paris 2000 years ago and from whom the city takes its name. It is a powerful reminder that the city of Paris has stood for thousands of years in the centre of a great cultural storm, and that countless people have fought and died to make Paris their home.
https://www.parispass.com/paris-attractions/Archaeological-Crypt-of-Notre-Dame.html
http://www.secretsofparis.com/heathers-secret-blog/beneath-your-feet-at-notre-dame-cathedral.html