The two underwater craft dive very deep to the ocean floor, where they discover a strange land populated by dragons, a giant octopus, and an eerie, undiscovered humanoid race.

There were various problems, including weather and the advent of talkies, which slowed/halted production several times before the film was finally completed and released three years later.

The film is loosely based on the back-story given for Captain Nemo in the novel The Mysterious Island, and might more properly be thought of as a prequel to Twenty Thousand Leagues Under the Seas.

[2] Until recently, only one reel with a color sequence was thought to have survived, in the collection of the UCLA Film and Television Archive.

In 2013, Deborah Stoiber from the George Eastman House film archive visited Prague to examine the sole existing color copy of The Mysterious Island.