I’ve always been fascinated with marble machines. These are those contraptions that have marbles moving up through a wheel or ladder and then descending via gravity through a maze. I remember seeing some very large versions of these large Rube Goldberg-esque contraptions in museums or airports when I was younger, and I would be mesmerized.
At the 2018 Maker Faire in San Mateo, I came across a booth by a company called Gualala Gadget. They had a table filled with 3D-printed marble machines running, and it was simply great. They had an email list, and after a few months they made some of their machines available to order. My wife gave me one as a Valentine’s day present on in February 2019, and after a little bit of assembly (mainly smoothing off some rough bits left over from the 3D-printing process) I had a working marble machine. The video above is of the model they call the Small Gear which you can order from their site fully-assembled version or a kit:
I really love this model because of how “busy” it seems. It almost borders on frenetic, and it makes me feel energized just watching it. They have some additional neat videos on the Gualala Gadget Youtube Channel also, and you can download STL files to print your own as well.