I love mechanisms. It's amazing how much mechanical complexity we were able to build before the advent of computers. Even more so when you learn how very minor changes like shaving a few degrees off an angle can be the difference between success and failure. As an embedded systems developer, I've been fortunate to work with a number of talented mechanical engineers over the years and come to realize that the complexity that they have to deal with isn't that far from what we have to do in software.

If you want to think in knots, go down the internet rabbit hole of investigating how the knotter in a hay baler works :-)

I love how so many mechanisms revolve (hehe) around revolutions - because that's the simplest form of mechanical effort to make and use.

I also love the accuracy you can get if you work on it - I'm thinking things like those giant castle doors weighing multiple tons, but a child can push them open if unbarred.