This is a great movie. It is very scary. It has a great story line. It also has great acting. It is one of the best movies I have seen. It is scarier then A Nightmare on elm street.

Down to the depths of the ocean floor, four members of a deep sea expedition find themselves trapped inside a huge cavern where the only way out is through a volcano. Of course, if by chance they make it out, they also have to think of how to get down that mountain, how to make it back to any sort of civilization, and how the two women on the voyage will keep their hairstyles oh, so perfect. Then, there's the mad survivor of a previous voyage, an old man who looks like he has the strength of a teenaged girl, who begins to lust after one of the two women, offers to kill the others so they can spend "forever" inside these petrified caves, and takes it personally when she thanks him but turns him down flat. Biology teachers might be interested in the first five minutes which explores the lower depths of the ocean floor, and there are some fascinating stock footage of various sea animals fighting, eating their pray, and just simply enjoying life at the bottom of the beautiful briny sea. Add in John Carradine as the inventor of the contraption they use to get way down deep, and you've got the makings of one of the few films that makes Ed Wood's epics look as if they were directed by Orson Welles. The rivalry between the two women is never fully explored other than for one of the women to tell the other that women simply just do not get along, especially where men are concerned. The acting is outrageously amateurish, and the quality of the film print is so grainy and distorted that everything looks like it's been preserved in negatives.

Four divers in a breakaway diving bell end up in a vast series of caverns. They explore their environment trying to find a way to the surface, but their path is blocked by an underground volcano. It is this cavern-world with its many stalactites and stalagmites that give this movie it's name.John Carradine is the scientist who's diving bell has failed. He realizes his mistake and makes a deal with his chief rival who is using a diving bell patterned after the first: he will correct his rival's design in exchange for using the bell at the first bell's location.This movie is weak, but not as bad as many reviewers have stated. There is little action, and the dialog is lacking. There is some suspense, however, as the four trapped people wind their way through the caverns. In addition, the caverns themselves provide a beautiful backdrop to this film.The flaws in the movie tip the scale to the turkey side. Carradine's character explains that the water pressure at the depth where the diving bell comes to rest will crush the divers, yet they inexplicably survive. The story explaining the hermit's presence faces the same problem.If you're a fan of John Carradine or Phyllis Coates, or if you enjoy movies set in underground caverns, you might enjoy this film. There is little appeal for anyone else.

One of my favorite sub-genres in the field of science fiction involves geological or subterranean motifs (I worked in the geological field for 11 years and loved every moment of it). Examples of these could be found in the works of Jules Verne, Edgar Rice Burroughs and Stanton Coblentz as well as other authors. Among SF films, examples of this are "Journey to the Center of the Earth", "The Monolith Monsters", "Unknown World", "The Land Unknown", "The Lost Continent", and others. This film by Jerry Warren is an example of this type of theme. Although the production values are based on a smaller budget than some other films, this is a very entertaining and stimulating film about explorers undertaking and expedition into the ocean depths. Due to circumstances, they end up within a network of subterranean caves with an air pocket. Eventually the party of explorers is rescued.The film has a lot to offer in terms of speculative fiction about the ocean depths, geology, and subterranean caves. Definitely a must-see.Dan Basinger 8/10