There is a somewhat sequel to this film called (aptly) "Journey to the Center of the Earth."
I have it; it's awful. Definitely a skull. Even having seen this prior, I mistook that version of "Journey to the Center of the Earth" as a failed TV show pilot. It feels slapped together from all sorts of quickly done stuff.
I almost gave this one a skull, but decided a few pieces of it were not totally worthless. The video announcer guy was actually quite funny, though most of his entertainment value comes during the ending credits (go figure).
I had vague memories of seeing this on MST3K, so I picked it up thinking that if nothing else, at least Kathy would be looking sexy. Yeah, me and my wishful thinking again. They apparently thought it would be a good idea to focus on her acting abilities instead. I'd recommend getting one of her exercise videos instead. "Absolutely Fit" is pretty good: Kathy looks really sexy, her voice isn't nearly as squeaky, and you get five abdominal workout routines to boot.
It's saying something when her workout videos are better than her movies. There are at least a dozen actresses that I cannot stand in a movie, but that I could watch (bikini-clad) jumping on a trampoline for hours.