Edgar Rice Burroughs' Pellucidar novels. I read them in my early 20s, they were fun then but would have been magic when I was 12. Short setup: the Earth is holl

Edgar Rice Burroughs' Pellucidar novels. I read them in my early 20s, they were fun then but would have been magic when I was 12. Short setup: the Earth is hollow, there's a sun at the center.