This area is called "La Plage".
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.
The lines that you see in the back are just the carbide lamps of a group of people going through while the camera shutter was opened. This is a long exposure shot (probably 3-5 minutes exposure). I went behind the pillars on the right and flashed several times from different places.
Fisheye, shot on film.