Paris Catacombs - National Geographic Magazine

From a series of photos by Stephen Alvarez
-- see slideshow on the Nat'l Geo article

National Geo writes up the Paris Catacombs, a 180-mile quarry under the city, from which limestone was mined to build major structures such as the Notre Dame Cathedral.

Not only is the history of this underground world fascinating, but also the illicit current-day exploring, gatherings and art happening down there.