Fortress is a very underrated sic-fi/action movie made in the early nineties by Stuart Gordon (the maker of re-animator/from beyond/dagon). The story is your standard prison movie formula, only it's set in the future.
The best thing about this film is the suspense of the action sequences. There were several scenes in the movie that literally had me talking to the TV. Nice performances by Jeffery Combs(as a very amusing computer geek type)and Christopher Lambert are a big plus. Kurtwood smith is also great as the prison director.
At the time it was released I was impressed with this film and over time my affection for it has grown (it continues to entertain even after seeing it several times). The main flaws would be the predictability of the plot and some cliché characters, but it's all handled so well that it doesn't really hurt the movie.
It's a good popcorn action movie, and one of my favorite Stuart Gordon Films. In my opinion, this is probably Gordons Second best film, after re-animator.