Seconded! Raytracer is phenominal, especially if you do it “purely” (no GPU/OpenGL/etc.). It’s relatively straightforward and the satisfaction of seeing even

Seconded! Raytracer is phenominal, especially if you do it “purely” (no GPU/OpenGL/etc.). It’s relatively straightforward and the satisfaction of seeing even a basic shaded sphere that you literally created from scratch in code by writing pixels to a bitmap file is awesome. I did this about a year ago and it was still one of the most fun/educational projects I’ve ever done.