It wasn't fun (for me) at first, because DS1 dismantled a kaleidoscope that I had made many years ago. The tiny pieces of cut glass that made up the colors were scattered on the kitchen floor. I calmed myself, asked him to be very careful while picking them up, and got some other things that we could put in the viewing end.
The kaleidoscope was made from a Pringles chip can, with a triangular mirror inside, a viewing hole (with rubber grommet for safety) at the bottom end, and the colorful glass baubles at the top end. It was similar to the one described in this kaleidoscope building webpage, but with the ends of the can intact. The clear plastic Pringles lid was taped back on to keep the tiny items in place.
Since DS1 took the tape off and opened the top, we had the opportunity to try other things inside it. Beads from a broken necklaces made nice black and white patterns because they were interesting shapes and completely opaque. Some semi-transparent beads and things with interesting silhouettes made fun patterns, too. The colored glass drops are the prettiest, in my opinion. We also looked through it (as a teleidoscope) at things around the house. This was quite fun also.