Enter Agartha. You've always known it was here, this strangeness familiar - the subterranean realm, the pathways to all space and time, and the doors, the doors, the doors! Things you may designate godlike or demonic roam the transdimensional corridors and cities. Hulking automatons patrol the way. Technology and magic interlock like a two-headed calf. The craft is beyond the scope of your species. Yet the clever secret worlder can learn to ride the anywhere paths to reach faraway places
—The Buzzing, The Secret World
Then, in 1938, a most remarkable realm of Innerspace revealed itself: the Hollow Earth. Ordinary men live on the outer circumference of the Earth, but unknown to human history, another innerworld was thriving on the inner circumference of the Earth! And at the heart of Innerspace, in the center of the planet, another sun casts its perpetual light on a perfectly spherical universe!
—Mage: The Ascension - Infinite Tapestry