Area 51
The famous Area 51 in the Nevada desert is a military installation at the Nellis Military Operations Area. But the base quickly became known as the most secretive military site in the world because it does not exist on any map or government website, leading many to craft conspiracy theories.
Some believe Area 51 is researching and experimenting on aliens and their spacecraft. More specifically, people think they are studying a crash that happened near Roswell, New Mexico, in 1947. Others theorize that the moon landing was staged at Area 51.
The government has said the facility is used to test experimental aircraft for the military.