Trade paperback #1 B.P.R.D.: Hollow Earth and Other Stories of the comic book series Bureau for Paranormal Research and Defense by Mike Mignola, creator of Hellboy, contains the short story Hollow Earth, where the team journeys into great caverns inside the Earth inhabited by Hyperborean people and fantastic machines.
The Marvel Comics features several underground empires in Subterranea ruled by villains like the Mole Man or Tyrannus.