In 1996 David Bell announced the very first metacell (eventually dubbed p5760 for its cycle length). I spent several days trying to understand it, having nothing but Bell’s incredibly terse sketch of its workings as a guide. Once I had managed to get a handle on it, I was strongly tempted to write up a more complete description for the edification of others – but this was a few months before I had my first web page. With no real outlet available to me, I abandoned the idea.
Needless to say, this essay resonated very strongly with me (although this was a far more polished explanation than anything I could have put together back then). Kudos to the author, both for the essay itself and for that perfect animated image at the top.
See also the Quest for Tetris: https://codegolf.stackexchange.com/a/142673
The ratio of words-read to words-understood in that essay is making me rethink my life right now. I had absolutely no idea how deep that rabbit hole went.
The book is amazing.