. . . this one particular o.o.p. tome, authored by the world renowned puppeteer (!) Walter Kafton-Minkel, no less, whose beliefs DON'T themselves include the Hollow / Inner / Under Earth "religion", lept to mind. Entitled "Subterranean Worlds: 100,000 Years of Dragons, Dwarfs, the Dead, Lost Races, & UFOs From Inside the Earth", it has to be THEE quintessential opus on the matter. It was published in 1989 by the now defunct Loompanics Unlimited. That publishing house was located in Port Townsend, WA. Have a look. It's an enjoyable, informative read, if nothing else . . . (+:-)}