The idea that there may be humanoid creatures existing in some unknown locations beneath the surface of the earth is so fantastic that it seems absurd. How could that possibly be? After all, the ground is pretty much solid mass and what we know of it gives us no reason to suppose that any such thing is remotely possible. When this notion occurred to me many years ago, this was my rational reaction. The old science fiction image of an earth that would allow journeys deep into its centre is patently impossible in light of contemporary scientific understanding. I gave it no further thought. Over the intervening years, with the revolution that has taken place in the understanding of earth's structure, with the discovery of new and even more unusual forms of life, and startling new archaeological, oceanographic and geological discoveries, it seemed that stranger things have been found. Perhaps the idea seemed so fantastic because earlier scientific models of the earth's history and structure were much cruder and simpler. Perhaps the underground is far more varied and complex than once thought. Perhaps the idea was not so absurd after all.