Showcase of a design/engineering artifact that is hiding in plain sight - Guilloche patterns. We see them every day, but never stop to evaluate why they exist. I always find a lot of joy out of exploring histories of things that we don't even realize are carefully designed.
Has to be run on an iPad Swift Playgrounds app.
Video: https://www.youtube.com/watch?v=UzRLZKDSB0I
There is also a simple version of the playground that will run as a Swift Playground on a Mac.