Pellucidar (1923) by Edgar Rice Burroughs is the second novel in his hollow Earth series. The story follows David Innes, who returns to the prehistoric inner world of Pellucidar aboard the iron mole invented by his friend Abner Perry. Haunted by debt and uncertainty in the outer world, Innes sets out to find Perry and reunite with his beloved Dian the Beautiful. Along the way, he battles the intelligent reptilian Mahars, their brutish Sagoth servants, and the treacherous villain Hooja the Smooth One, while striving to unite primitive human tribes and build an empire of freedom and enlightenment.
