What is the Hollow Earth theory?

   According to the hollow-Earth theory, a race superior to our own lives somewhere beneath the surface of the Earth. Some proponents of this theory base their arguments on the existence of UFOs, which they say are not from outer space but from innermost space, and on some ambiguous comments made by Adm. Richard E. Byrd after he flew over the two poles.
   Though no one has ever located them, entrances to this fabulous world are said to exist at both poles.

The Hollow Earth