Most of the action takes place in Pellucidar, Earth's inner world, which is a vast place with oceans and continents of its own. In this strange realm, Burroughs has unleashed his imagination to run free of the natural restrictions of Earthly lands such as Africa, where the setting, conditions, and creatures need to conform to what is known about the country. Burroughs makes excellent use of this imaginative freedom to populate Pellucidar with fantastic denizens—devising new species of intelligent beings, mixing prehistoric animals with creatures of his own invention, and conjuring up exotic locales to suit the needs of his plot. For instance, when David and Dian need some time together to forge their bonds of love, nearly impassible mountains appear where they can live together isolated from the events of the rest of the world.

The "buried city of Phutra" is a fine creation inhabited...