These days Paris catacombs are no longer used. The city does offer tours, but only around a small area of these expansive underground tunnels.
That's not good enough for these inquisitive photographers known as Urban Explorers. They headed off the beaten track to take a look around the areas that most tourists never see.
Check out their stunning photos of a world that many people don't even realise they're standing right above.
From the Upcoming ueue, submitted by .