As you may have guessed by the title of this blog post (and the previous one), I’ve assigned myself the duty of exposing the underworld to you, Coolest Stuff readers.

So what’s today’s mysterious underground site? It’s the once top-secret bunker buried beneath the upscale Greenbrier Hotel in West Virginia.

Here’s its story: Between 1959 and 1962, during the Cold War era, the U.S. government had the hill beneath a future addition to the Greenbrier hotel hollowed out. Then it had the hole filled with 50,000 tons of concrete. About 4,000 loads of concrete were hauled to the site by a supply company, and the bunker’s two-foot-thick walls were reinforced by steel. Two of the vaultlike doors installed at the site were each 12 feet, 3 inches high and 15 feet wide, and weighed 28 tons. These and other odd design features led nongovernment workers to assume one thing: The hotel was building a bomb shelter — a really, really big one.