Watch Unknown World (1951) Free Online

Dr. Morley (dubbed the Prophet of Doom by at least one newspaper reporter) is an obsessive opponent of all things nuclear. Fearing that atomic weapons will destroy all life on earth, he recruits a group of scientists for his Society to Save Civilization, and they make plans to find a living space deep within the earth where man can survive and rebuild from the nuclear holocaust they see just over the horizon. After the group fails to secure any funding, a rich newspaper publisher's son forks over the cash and accompanies them on their monumental journey. They design a cyclotram, basically a great big ugly metal boxcar with a humongous drill for a nose, ascend to the top of an extinct volcano, go down into the crater and start drilling through rock as they make their way downward. Every so often, they stop for a minute to fight or to provide an opportunity for one of them to die.