An eccentric geology professor acquires an old book and hidden within its pages finds an ancient parchment. On it is a coded message that reveals directions to a secret passageway that leads deep within the earth's interior. The professor immediately sets off on a daring journey to Iceland, where he and his companions enter into an extinct volcano and make their way to the center of the earth. They soon find a strange underground world where the laws of science are turned upside down. They discover huge caverns, luminous rocks, a subterranean sea, primitive forests, and fearsome prehistoric creatures that time had forgot. The travelers encounter one stirring adventure after another as they explore deep within the bowels of the earth.