The manhole opens on a street sidewalk in the center of Paris. This is one of the secret access shafts to the off-limit underground network.
Catacombs of Paris (off-limit area), about 20 meters (60 feet) underground, under Paris city center.
This is a part of the 200 Km network of ancient tunnels not opened to the public, but regularly visited by trespassing urban cavers called "cataphiles". See more information in the album description.