This is an unusual entry in the Hammer Films catalog—a bizarre mix of fantasy, adventure, and science fiction, full of obviously fake special effects, a plot that doesn't quite make sense, over-the-top performances, and plenty of exposed skin! The story, such as it is, involves a cargo ship carrying dangerous goods and its passengers, captained by a very intense Eric Portman. They fall prey to a mutiny and end up adrift in the Sargasso Sea. But then they discover an island that seems like a rescue, except it turns out to be a place stuck in time, ruled by cruel Spanish conquistadors. And the surroundings are teeming with dangerous creatures, including aggressive seaweed. Adapted from Dennis Wheatley's novel *Uncharted Seas*, this film will have grown-ups questioning their sobriety, while younger viewers will enjoy the bright colors and cheesy monsters. It’s a very strange experience, silly in its own way, and it doesn’t quite reach "Z" grade movie status, but it is entertaining—though even those of us who like to drink might never be able to completely get into its craziness. 7/10

Source on TMDB