Could you give more details about the creatures they encountered, etc.? There are lots of "lost world" movies like this. Heck, it could be
The Incredible Petrified World, which has a submarine and a mixed sex crew finding a lost world in some undersea caverns, but I doubt that film would have made much of an impression on you.
Also, why is the "javascript:void(0);" in your thread title? I guess it was copied and pasted from something?