At the Earth's Core (1976)

Synopsis
This is the second sci-fi adventure based on a novel by Edgar Rice Burroughs, the first being 1975's The Land That Time Forgot. At The Earth's Core stars Doug McClure as explorer David Innes and Peter Cushing as professor Abner Perry, whose experimental "iron core" drill goes out of control and leads them to the underground kingdom of Pellucidar, where the Wing People are ruled by the monstrous, flying Mahars. With the help of the professor, Innes leads the Wing People in revolt against their evil masters. Monsters and mayhem abound in what is essentially a well-produced, if somewhat juvenile, knockoff of The Time Machine. ~ Don Kaye, All Movie Guide