This was interesting information about Atlantians living in a place called Agartha inside the earth which is hollow. The truth is we have not been to the center of earth and have just hypothesise that the earth should have a molten core.
The reason being when earth was born it was very hot, gradually it cooled down on its surface but the inner core is still hot, filled with molten metal. There are unexplained holes present in some regions of earth especially in south and north poles which are suppose to be outlets for this inner world. Truth is stranger than fiction lies true in this case. In ancient manuscripts the hollow earth is mentioned, this could be true unless and until we find it ourselves. But if this is the truth then the secret organisation like Illuminati must be aware of this.