Area 51 is a base located in southern Nevada that is tied to many UFO sightings. The base is believed to be a location that was formerly used by the United States Government to research and reverse engineer extraterrestrial spacecraft technology.
It is also believed that there may have also aliens bodies from previous crashes. The base is monitored 24/7 by vehicles and signs are posted miles away from the facility saying it is a restricted area and that photography is prohibited.
There have been former scientists who have spoken out publicly about Area 51, such as Bob Lazar. The US Government shares very little information on the base and in their internal maps the base is not listed.
After the huge popularity of Area 51 it is believed that this base is no longer in operation and these operations have been moved to other secret locations.