Jerry Warren made this one. What more can I say?
A team of Fifties SF movie scientists takes the first descent on a Bathysphere, only to have the cable snap, depositing them at the bottom of the sea. There they find a natural, air-filled cavern system (which may or may lead to the surface) and try to explore it in the hope of finding a way to the surface.
The film never commits itself to how deep they are, or why a cave in rocks made primarily of iron looks like a limestone cavern. The explorers get out of the Bell in their wetsuits without being crushed, then spend a lot of time wandering around in Colossal Cave Mountain Park in Arizona…
It’s slow, it’s talky, it’s extremely cheap,not a lot actually happens, and John Carradine, despite his top billing, mostly spends his brief onscreen time talking.
One does have to wonder, though, whether this is the same physically impossible cave at the bottom of the sea that was home to a secret government program in The Rift [aka, Endless Descent](1990)? I guess they didn’t want a discovery like that to go to waste.
rivets on the poster 