Gilgamesh, Alexander the Great and Moses all traveled to find the fountain of youth. Gilgamesh and Alexander both came close, but to get there the had to go inside a mountain, into a cave and then deep, deep deep into a subterranean world.
Also note that one of the initial annecdotes in the book speaks of a "god" who has died and who also travels to an underground world of secret, hidden, subterranean passage ways to get to one location where the chariots of the Anunnaki blast off. To facilitate lift off, the gods would activate a system of levers and pullies that would open the mountaintop almost the way elevator doors part.
Perhaps this doesn't entirely advocate the veracity of hollow Earth theory; but it does at least suggest that the Anunnaki were highly capable at tunneling and building subterranean bases and living quarters and did so quite extensively.
(Edited by George Hayduke at 3:11 pm on June 21, 2007)