Far from being a modern, internet crackpot idea, hollow earth theory has walked a long and winding path, many centuries old. From the mythological pits of hell, to the pseudo-scientific theories of the enlightenment, right through to modern science fiction, founding philosophies of utopian cults and even tenuous links with the Nazis, the proponents have been many and the theories varied, though whether or not they were ever anything other than crackpot is a different question altogether.