MacGuyver, if you're still looking for ideas related to 4-D, you could consider showing projections from an on-site video camera with 'memory' -- meaning active movement comes to the forefront but otherwise the picture doesn't change, similar to taking a photo with an open exposure. If you think of our world as 3-D + time (aka movement through 3 dimensions), this is a way to visualize such on a 2-D screen. I saw a setup like this at our local children's museum and it was pretty fascinating, even if I cannot describe it very eloquently.