http://www.ourhollowearth.com/OurHollowEarth.htm
Hahaha! Loon city. When I was a kid, the "Hollow Earth" theory was best represented by Edgar Rice Burroughs, author of "Tarzan", except it was named Pellucidar and populated by dinosaurs and cavemen. There was light and heat from a magically suspended micro-sun in the exact center. It was never night time there. The heroes of the books battled Thak and Grog, evil cavemen, and wild beasts, to save the half-naked, beautiful women who were always in trouble.
Then I learned physics, and my beloved Pellucidar became impossible, because there'd be no gravity inside a hollow sphere. Thak and Grog would float around, and the microsun would rattle around like a bean in a maraca.
