Photo Gallery: Stephen Alvarez’s Paris Underground

American photojournalist Stephen Alvarez explores the hundreds of miles of tunnels that comprise the Paris underground for the cover story of this month’s National Geographic. While many of these locations (like The Catacombs) are open to the public, some of Paris’ quarries have been strictly off-limits since 1955; rule-breakers, also known as “cataphiles,” have used these subterranean spaces for everything from creating art to throwing wild parties to scuba diving (!) to simply exploring unmapped territory. Click through to take a look.

The Catacombs. Photo credit: Stephen Alvarez. [Image via designboom]