Pierre Cathedral in Geneva, Switzerland, is John Calvin's home church. In the 1990s, they renovated it, and part of the process was to remove the floor. This revealed multiple layers of ruins beneath, of previous smaller churches (you can clearly see a round baptistery, for example).
I love this photo, because it shows how our current church is built on the foundations of our forefathers.
Photo credit unknown - this was a postcard we purchased at the cathedral, that I took a picture of