The biggest archeological site under a cathedral in Europa. A visit takes you back in the time. The first monument on the site was for a pagan hero, afterwards a church was constructed on the grave of the pagan hero. Lots of different remnants are visible. I especially enjoyed the mosaic floor of the bishop.

Archeological Site at St. Pierre’s Cathedral, cour de Saint-Pierre 6 CH-1204, Geneva 1204, Switzerland
http://www.site-archeologique.ch/
+41 22 311 75 74

Visited November 2012. You can find my review about Archeological Site at St. Pierre’s Cathedral also on TripAdvisor.