At the Earth's Core by Edgar Rice Burroughs is a fantasy novel, the first in his series about the fictional "hollow earth" land of Pellucidar.

In this, the second book of Burroughs' Amtor series, Napier travels over perilous mountains and through forests, inhabited by creatures more terrifying than any nightmare, in search of the lovely princess Duare, who has been snatched from his arms. In the Room of the Seven Doors, Napier faces the choice of his life. Six doors led to terrible deaths—the seventh is the door to life. But for him, this door too leads only to new dangers on a planet whose beasts and men are more frightful than any that stalk his native Earth.

In the wild, unexplored coastal jungles of West Africa lives a wild human boy named Tarzan, the adopted son of a tribe of fierce almost-human anthropoid apes - but in reality, the unknown heir of a wealthy and titled English noble family. Then one day, a small party of American treasure-seekers is marooned on Tarzan's beach, including a lovely Baltimore belle named Jane Porter.

Bowen Tyler, his reluctant crew and a blonde heroine, find themselves marooned in a nightmare world of mighty dinosaurs and bestial apemen who kill on sight. This is the lost continent of Caspak, a hot, dark and mysterious prehistoric world located somewhere in the icy waters of the Antarctic. Their only hope of rescue is a note in a bottle flung into the sea. The survivors persist and penetrate the heart of Caspak to find the incredible secret that claws, fangs and spears have guarded since the beginning of time.

Barsoom Series Collection: 7 John Carter Stories is an audiobook collection of seven novels/stories of John Carter by Edgar Rice Burroughs. It will transport you to a fascinating new world unlike any other. Join John Carter as he finds himself on another planet beyond his deepest imagination - Mars, with almost a complete lack of resources.