I first got a computer back in the early 1980s - a Sinclair Spectrum. You either copied programs from magazines by typing them in on the little rubber keyboard, or loaded saved programs from a cassette tape. After doing both of these for a few weeks, I started to read the manual and slowly learned a little programming in Sinclair Basic.
This was the first thing I made which ran successfully. Just drawing a line which followed a sort of square spiral and relying on a drawing function which only turns on a pixel if the original pixel is blank. It's fascinating watching simple rules produce complex outcomes. It was one of the first things I tried to reproduce when I discovered the processing language.
Play with the code here.