At The Earth’s Core by Burroughs, Edgar Rice

At the Earth’s Core is Edgar Rice Burroughs first in his series about the fictional “hollow earth” land of Pellucidar. “In their newly invented mechanical mole, David Innes and his friend Abner Perry penetrated the world’s crust and traveled five hundred miles down towards the center of the Earth. But instead of meeting the eternal fires they expected, they broke into a new world more strange and terrifying than the certain death by fire they had expected. “For this was the inner surface, the land of Pellucidar, where evolution had taken a strange turn and man was slave to the monstrous Mahars. In a world where time and direction did not exist, David and Perry fought for existence against prehistoric dangers and the chance to bring civilization to this world of Eternal Noon.