Pellucidar
"Pellucidar" by Edgar Rice Burroughs. Public domain in the United States. Source: https://www.gutenberg.org/ebooks/605. Text and audio edition: LivingBooks.
"Pellucidar" by Edgar Rice Burroughs. Public domain in the United States. Source: https://www.gutenberg.org/ebooks/605. Text and audio edition: LivingBooks.