Vril, the Power of the Coming Race

VRIL follows a young Englishman (the narrator), who accidentally finds his way into a subterranean world occupied by beings called the Vril-ya. He discovers that the Vril-ya are descendants of an antediluvian civilization who live in networks of subterranean caverns, where they make use of an "all-permeating fluid" called "Vril", a source of tremendous power. The Vril-ya seem to be expanding, and they are running out of space under the ground.