Area 51

The  is a military base in Nevada. Little is known of it, apart from the fact that it exists.

Appearances
is mentioned in the original Fallout, as a print on the crashed UFO in a special encounter. It was also supposed to appear as a location in one of the early drafts of Fallout 2, inhabited by a group of scientists.

It is also possible, that the Area 51 will appear in he upcoming Fallout: New Vegas.