Operation Earthworm — Joe Archibald

Though fans of classic science fiction will definitely enjoy this short story from Joe Archibald, its focus isn't on travels to the farthest reaches of the universe. Instead, the tale is concerned with what a character terms "inner space" -- in other words, the mysterious depths of Earth itself. A miraculous device known as the Magnificent Mole allows explorers to journey to previously undiscovered marvels of the subterranean world.