I love Stirling Engines, not only do they make awesome conversations pieces, but they’re a lot of fun to build. The HB26 Twin Bridge Stirling Engine Kit ($283) is a great example of an engine that will provide you with hours of enjoyment. It features massive polished brass wheels and cylinder, and stainless steel guide components, and screws. It comes with about 80 pieces, so set aside about 3 hours to assemble. From one fill up, you get about 15-20 minutes of run time. Check out the video below to see it in action.