I have been reading a lot about arctic customs and myths over recent months. I’m working on an adventure idea for my D&D campaign setting, The Isles of Ethos, which will take my players into the icy north. Many of the myths of the Inuit are fascinating and have spawned lots of ideas for my game, but it was a more western concept that has caught my attention. The Hollow Earth Theory. First off I should say that I don’t think it should be called a "Theory" - it would dignify this pseudo scientific hogwash with the trappings of legitimacy - especially as this myth is still perpetrated to this day by Internet kooks and shysters. However there was a time when the idea that the Earth had an inhabited inner world did not seem so ludicrous.
The Hollow Earth concept is an ancient one, and for many centuries made some sort of sense as the home of Hell, Svartalfheim, Hades or other subterranean realms. The idea had many proponents even into more modern times, including Edmund Halley on 1692, and even (in part) prompted the19th century US Polar expedition of 1838-1842.
In the 20th century the Hollow Earth myth was explored by the Thule Society which had close links to Adolf Hitler and the Nazi fascination with the occult. There are even theories that Hitler ordered a research journey to the Arctic to find an opening to this inner world. This is partly based on the claims of Admiral Dönitz who spoke during the Nuremberg Trials of "...an invisible fortification, in midst of the eternal ice". I hasten to add (in case my players are reading this) I’m not using this idea in my game but it would make a great game in its own right. Indeed Exile Studios produced the ENnie nominated Roleplaying game Hollow Earth Expedition in 2007. HEX is set in the 1930s where secret societies and villainous organizations (including the Thule Society) have a vested interest in the Hollow Earth. As usual my game design research has lead me on a major tangent away from its original focus, and I don't think that's such a bad thing. In fact I'd go so far as to say this is one of my favorite things about game design and writing: you never know where you'll end up.