Unknown World (a.k.a. Night Without Stars) is a 1951 independently made American black-and-white science fiction adventure film, directed by Terry O. Morse, and starring Bruce Kellogg, Marilyn Nash, Jim Bannon, and Otto Waldis. Distributed by Lippert Pictures, it was produced by Irving A. Block, Jack Rabin, and Robert L. Lippert.

The film’s storyline concerns a scientific expedition seeking livable space deep beneath the Earth’s surface in the event a nuclear war makes living above ground impossible.

Plot
Dr. Jeremiah Morley (Victor Kilian) is concerned about an imminent nuclear war. He organizes an expedition of scientists and has them use a large atomic-powered tank-like boring machine, called the Cyclotram, capable of drilling down deep through the Earth’s surface in order to find an underground environment where humanity could escape and survive a future nuclear holocaust.

The expedition (Jim Bannon, Marilyn Nash, Otto Waldis, Tom Handley, and Dick Cogan) begins after government funding has fallen through, and they are bailed out at the last minute by private funding from a newspaper heir (Bruce Kellogg), who insists on going with them as a lark. Romantic rivalry soon develops between Bannon and Kellogg for Nash, and during the dangerous underground expedition two lives are lost to the perils of their adventure.

In the end the scientists accomplish their goal and find an enormous underground expanse with a plentiful air supply, its own large ocean, and phosphorescent light. However, all the lab rabbits brought with them give birth to dead offspring. Through autopsies, it is discovered that this strange underground world has somehow rendered the rabbits, and hence any other life form, sterile. Dr. Morley is deeply depressed by this news. When an underground volcano suddenly erupts, he fails to enter the safety of the Cyclotram and quickly perishes.

The Cyclotram, carrying the remaining survivors, enters the underground ocean to avoid the eruption. They soon find themselves rising toward the surface of the upper world, having been caught up in a strong, upward-moving ocean current. They eventually break the surface near an unknown tropical island.

Cast
Victor Kilian as Dr. Jeremiah Morley
Marilyn Nash as Joan Lindsey
Bruce Kellogg as Wright Thompson
Otto Waldis as Dr. Max A. Bauer
Tom Handley as Dr. James Paxton
Dick Cogan as Dr. George Coleman
Jim Bannon as Andy