This interactive art piece from Italy/Portugal-based architects Moradavaga, called HEUREKA!, is basically a very large kaleidoscope that you operate manually by turning bicycle wheels. It is certainly not the simplest kaleidoscope ever made, but it is among the coolest. Moradavaga conceived it as a "thinking space," so that instead of taking a long walk, you can now just head over to the bicycle wheels, stick your head inside the wall, and talk the crank while contemplating all the different shapes and colors.
This does not seem like the most efficient kaleidoscope
But it might be the coolest kaleidoscope