This is called the catacombes, it's illegal to visit them, you can 1. get lost and 2. find a secret theater. I'm not kidding you.
I've dreamt of visiting them as a kid but now I don't like the possibility of getting lost with strangers (there is always at least 10 living person in there, I've heard) in an underground tunnel where my cell phone won't work.
It's not illegal to visit them, they charge an entry fee for a certain section and only let a few people in at a time so the queue is very long, I think I waited an hour and a half. Was one of the best places I visited in Paris, highly recommend.
“Why??”
*dog drooling: “ummm I have a flair for French cuisine”
I've dreamt of visiting them as a kid but now I don't like the possibility of getting lost with strangers (there is always at least 10 living person in there, I've heard) in an underground tunnel where my cell phone won't work.