In the 18th centuary, when the cemateries of Paris ran out of space for the dead, the city began to store the bodies in vast underground catacombs.
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 .