I've been through this one in hungary:
http://www.labirintus.com/en/1
It's more of a labyrinth, but the cool part is the attraction which would NEVER be allowed over here in North America because of insurance problems: You have to navigate the whole thing with an oil lamp... Not some electric lamp, not a flashlight: An oil lamp. It's a couple kilometers walk, but there are gates blocking off these sections of the
tunnel that branch off for hundreds of kilometers underneath Budapest. It's awesome just to think about. Freaky going through these tunnels at night with an oil lamp. And they don't bother exterminating mice bats or snakes either... You're on your own
But it's 100% legit.