When I saw this engine on Amazon I was fascinated. At first I was looking for a desk ornament but this was much better. It looks good and it's functional.
Here's a photo of my Stirling engine set on top of an insulated coffee mug. It works great and I had it running for 4 hours one time. That was the longest time for me.
I placed it on a dish filled with crushed ice instead of a coffee mug, it still worked! With ice cubes on top and a coffee cup at the bottom it goes faster.
This video explains how it works: