For the past several days I’ve been enjoying solving successive levels of Euclid the Game, an online set of puzzles based on Euclid’s Elements.
You are initially given the equivalent of a stick, a straight edge and a compass (tools for drawing points, lines and circles), and are asked to construct an equilateral triangle. Once you’ve solved that, you now have a new tool that draws equilateral triangles, which you use to help solve the next problem. As you solve successive problems, you build up a collection of increasingly sophisticated tools, and solve increasingly difficult problems.
I’m currently on level 20. Not sure how far this goes, but let me know if you get stuck.