There are a myriad of conspiracies concerning "Hollow Earth". Some people contend that the earth is really hollow inside and that there are 1400 mile diameter entrances at the north and south poles. Both of these entrances are said to be usually covered in clouds and the airspace is restricted by law. The earth's crust is supposedly 800 or so miles thick and then after that you reach inner Earth.

In mythology the name given to this inner Earth is Agartha. There is said to be a sun in the center and there are vast civilizations with great technology and natural resources. There are also said to be many extinct animals such as dinosaurs and mammoths that exist there.