YouTube's TheInternetFTW shows off this arithmetic logic unit (ALU) that he's built out of blocks and chunks in the game Minecraft. It's part of a larger "Hack" computer (as described in Elements of Computing Systems).
So basically, this is a computer subcomponent that you can run around on, physically moving around and watching as it does its thing. It's the 21st century equivalent of the wonderful Bell Labs Cardiac Computer that I played with as a child — a cardboard computer that got me interested in computing when I was six or seven. It is the virtual made visceral, an unpacked microscopic mystery. It is sheer genius, better than any ten boring lectures on ALUs, computing theory, Boolean math, etc. It's the kind of thing that makes me wish I was a kid today, and glad that I have a kid of my own.
(Thanks, Fipi Lele!)