Where to Watch At the Earth's Core (1976)

4,000 miles to the center of the Earth to a world within a world

A huge burrowing machine tunnels out of control at ferocious speed, cutting clean through to the center of the earth, to the twilight world of pellucidar. Once there, Dr. Perry and David Innes are threatened by half human creatures, lizard-like birds, and man-eating plants.