4. The Nevada Triangle.
Our final triangular entry on the list, the Nevada Triangle marks a 25,000 square mile stretch of desert and mountains in the state of Nevada. This desolate stretch is in the vicinity of the notorious Area 51 military zone, and has been the site of a number of disappearances. The most famous is fairly recent, when famed aviator and adventurer Steve Fossett in 2007. Fossett flew into the triangle in a small plane and vanished without a trace, despite a massive search effort.