Last time the three things meme came up I concluded that my most interesting things are more "three unusual things I have done with people who don't happen to read my LJ" than three things I'd done on my own. But on reflection there are some things I think I can put down which won't be quite as much a function of which social circles read this blog. So...
Three things I've done that I'd be surprised if any of my friends (on LJ or otherwise) had:
Made an astronomical observation with an optical telescope of >5m aperture
Gone on a >1000km bike ride Edit: Finished last in a multi-day bike race
Competed in a motorsport by writing a computer program