It looks like there are two giant water propelled-gears which come together and force them onward, climbing up a stairway.
I knew there would be water-based traps. None of the others have used this. Perhaps when Spielberg was checking out the Wii at gaming comference in Caifornia a couple years ago, Miyamoto exposed him to the brilliance of the water temples in Zelda. I think we can expect many different, elaborate, water-based traps. I know they did this in 'National Treasure', but this will be undoubtedly tentimesbetter. The only thing as mechanically intriguing as a rolling-ball chasing you, is trying to figure out where a multitude of water will go, what it will do, and how to stay out of the way.