I spent all day twiddling nipples.
Or rather, I was learning how to make a bike wheel given the component bits (nipples being the bits that attach the spokes to the rim). By the end the wheel I was working on was reasonably true, just the odd annoying slight radial bump I couldn't work out how to remove, and reasonably taut, maybe not quite as much as it could have been, but I was happy with it. I'm also quite pleased with myself for doing something constructive and manual, I've never thought myself to be much good at that sort of thing.
I can recommend the courses which David Green occasionally advertises on cam.misc, he knows his stuff and is a good teacher. I now feel all enthusiastic about bike wheel maintenance and have good ideas for what to ask my family for birthday and christmas presents (truing stand, dishing gauge etc.).
...however I got back, had dinner, started writing this then shut down for a couple of hours as my body demanded some pay-back for a late night followed by standing around learning new physical skills all day. Urgh... very tired.