Located near the Denfert-Rochereau station of the Paris Metro the catacombs are a true descent into Paris's past. When the graveyards became full to the point of posing health problems in the late 18th century, the residents were moved to quarry tunnels below what is now the southern part of the city. After descending over 130 steps down a small spiral staircase, you navigate a series of long, dimly lit, often low tunnels. Be prepared to duck to avoid hitting your head in one of the many low areas. Once through the brick and rough cut stone tunnels, you reach the catacombs. Here, walls are lined with compactly stacked bones, leaving only four feet or so to walk along many areas. Wear a hat, as water drips from the ceiling in many places as you explore the myriad of rooms and tunnels, while being watched by the empty eyes of skulls arranged both on and in the stacks of bones. Perhaps not for the squeamish, this can be a delightful tour unique to the old world, and an opportunity for some great photos for the well equipped photographer. Flash photography is not allowed, however, so a steady hand and knowledge of low light photography is needed in the dark tunnels.

Near Luxembourg gardens. Just ask someone if you cant find it, most people will know. Get there early, the line can get really long. It closes at four so make sure you get there (if you want to see it then) around 230ish otherwise you may miss out due to the wait. Quite cold as its very far underground so take a jacket or put up with it for the hour or so. Even if you are claustrophobic, put up with it, its worth it.

Macabre but fascinating, this is definitely one thing to see in Paris.  The tour takes you deep underground through tunnels lined with bones and they explain that this is one of the places that the French Resistance met during the war- to be honest the thought of hiding down there knowing your life was at risk and without electricity doesn't bear thinking about!

If you're looking for a creepy experience, this is it. This is probably one of my favorite places in Paris...call me weird, but how many other places are there where you can see crosses made from human skulls? Not many. Just be prepared for lots of stairs and lots of walking.

Very freaky place, in the 1700's and 1800's cemeteries were becoming full and so they used to clear them. These underground tunnels contain over 6 million Parisians, not for the faint harted but definetly worth a look if you like the unusual.