The Dead Pit (1989)

Summary from IMDB:
A renegade doctor is shot dead and entombed with his fiendish experiments in the basement of an abandoned wing of a mental hospital. Twenty years later, a mysterious woman is admitted with amnesia, and her arrival is marked by an earthquake - which cracks the seal to the Dead Pit, freeing the evil doctor to continue his work.

My take on the movie can be found at my main blog.