"Pellucidar" is a fictional setting created by author Edgar Rice Burroughs in his series of novels. It is a prehistoric world located inside the Earth, characterized by a vast, sunlit interior with a flat landscape and a central sun. The inhabitants include various primitive tribes and prehistoric creatures, creating a unique ecosystem. The first novel, titled "At the Earth's Core," follows the adventures of David Innes and his companion Abner Perry as they explore this underground world. They encounter challenges from both the environment and its inhabitants, highlighting themes of survival and discovery in an uncharted territory.