So, this isn’t exactly retrocomputing and it looks like it’s from four years ago, but I just found it and thought that many here may find it interesting.
This guy built a simple 8-bit CPU out of essentially discrete logic circuits (from what I’ve see so far, nothing more complex than a 4-bit adder chip) and explained the entire process.
I remember reading an article a while back about basically computing using cards which block or allow light to flow as a series of logic gates. Another way to think of it is reinventing the punch card.