The Crypte below the square of Notre Dame was really interesting to visit. It depicted the growth of Paris from when it was just a tiny fishing village to what it is now.
The ruins uncovered beneath the square of Notre Dame are Roman-era homes. They also serve as a good example of how the level of the ground has been raised over time; the tops of these ruins are a good 10-15 feet below the current street level. Maybe more.
Using the flash on the ruins just flattened all the detail, so here they are in all of their orangey goodness.
These are four column capstones that all date from different periods in the city's history.
A Roman house. Nice archway.
A well and some exterior walls of houses (M).
This is the one I think is amazing. The square column of bricks to the right of the archway in the middle of the picture? That's an air duct for the furnace that they made from naturally occuring hot air and terra cotta "air ducts" that led throughout the house. Astounding.
I think that's what this picture is, anyway. If not, that concept existed in the next set of ruins. And I still think it's amazing.