I started building one of those Cloud Chambers from the original Scientific American magazine. Never got completed. At age 17 I didn't have the knowledge or resources to do it but I was fascinated by the whole idea. And I had a watch with radium numerals !!
Built a Van De Graaf Generator a few years later when I learned a bit more technical stuff. That was fun !! From the same magazine, another edition though.
And Sugar\Permanganate rockets .... messy.
Here you go, Build a Cloud Chamber !!
http://www.scienceinschool.org/2010/issue14/cloud
Piece of cake