A while ago, I ran into this bit of artwork at the Amersfoort trainstation:
It's a digital aquarium with goldfish in it, projected by a Panasonic projector from the roof of the hall. But there's a catch; the water moves interactively when you walk over the screen:
Even the fish are trying to evade those who walk over/through the water.
How? By using a motion sensor above the screen (the box in the middle), hooked up to the computer driving the projector.
The speaker next to it plays watery sounds as you walk by.
All in all a nice piece of work, and it's a real attraction to children.
Cheers, K.