It's a cool tour if you ever get the chance to take it. The retaining walls are built primarily of stacked femurs with skulls interspersed. Eventually the people stacking the bones got whimsical and the designs get more elaborate and weirder the further you go. The walls aren't very high so you can easily see over them into the bone pits.

The tour was in French, no translations. I was maybe 13? We happened to have a bunch of historians in the group that day so there was a lot of extra information. The two things that stick with me most are one of them pointing out a hole in the wall where a skull should be and saying that this gap wasn't there last week. There are weirdos taking skulls from the catacombs. The other thing I recall were these two ladies from Tennessee. One of them jammed a long, gaudy, fake nail right into a skull and said, "Lookit that!" and I just looked at her in disgust and told her, "There are signs everywhere saying not to touch that... and it's a dead person's skull." Up to that point, I don't think she realized I was also American and spoke English. What a freak.

One of the things on my list is to do the illegal tour (bribe a historian) and get invited to the screenings held down there.