This little easy-to-make paper sculpture can be turned inside-out over and over while you watch it change colors. You can find free detailed instructions on how to fold this printout at Simon Quellon Field's site called Science Toys You Can Make With Your Kids. It was designed years ago by a bored mathematics student. The toy is called a Kaleidocycle, or Flexahedron. It goes together quickly, and can keep you happily fidgeting with it for hours! While you're there, check out some of the other cool toys you can make with things you've probably got laying around the house!
That's ridiculously cool!