A kick arse movie about a group of people trapped in a maze of cubic rooms. Some rooms are safe but if you step in the wrong one you get sliced into chunks by a wire screen or have your face melted in acid. The only clue they have to what it all means is some numbers on the doorspaces.
But it's not a shitty teenage horror movie like Saw where someone dies every 2 seconds and there's no plot. The film is actually pretty clever and if you want an original film, Cube is what you're looking for.
Don't say Cube is bad because it was shot in 1 room. The room changes colours and it actually feels like there's a lot more than there actually is. Look at the original Star Wars series. It was only set on 7 planets, but it felt like a lot more, and that was a great series, just like the original Cube.
But DON'T see the sequels. They suck.