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

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.

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.

[citation needed] Unknown World was put together by two Hollywood special effects men, Jack Rabin and Irving Block, who are two of the film's three producers.

[citation needed] The B-Movie Review site Million Monkey Theater observed that the "production crew try hard, and it really seems like they have an important message to tell, but the execution and polish are lacking".