Area 51. It's the most famous military institution in the world that doesn't officially exist. If it did, it would be found about 100 miles outside Las Vegas in Nevada's high desert, tucked between an Air Force base and an abandoned nuclear testing ground.
Then again, maybe not-- the U.S. government refuses to say. You can't drive anywhere close to it, and until recently, the airspace overhead was restricted--all the way to outer space. Any mention of Area 51 gets redacted from official documents, even those that have been declassified for decades.
It has become the holy grail for conspiracy theorists, with UFOlogists positing that the Pentagon reverse engineers flying saucers and keeps extraterrestrial beings stored in freezers. Urban legend has it that Area 51 is connected by underground tunnels and trains to other secret facilities around the country. In 2001, Katie Couric told Today Show audiences that 7 percent of Americans doubt the moon landing happened--that it was staged in the Nevada desert. Millions of X-Files fans believe the truth may be "out there," but more likely it's concealed inside Area 51's Strangelove-esque hangars--buildings that, though confirmed by Google Earth, the government refuses to acknowledge.