What are some horizon-expanding weekend undertakings?

There are some books that you can read, some projects you can do in a weekend or two that expands your horizon. Like:

1. Raytracing in One Weekend (https://raytracing.github.io/books/RayTracingInOneWeekend.html)

2. Think OCaml (https://greenteapress.com/thinkocaml/)

3. Let's make a Teeny Tiny compiler (https://austinhenley.com/blog/teenytinycompiler1.html)

What are some more?