I'll be in Washington DC at the end of April for DASH. What should I see while I'm there? I've already seen a lot in the area on a previous trip when I put my socks on my ears. But what else should I do? The usual travel guides don't seem to know about, e.g., the Ravenchase/ClueKeeper Washington DC Hunt, so I'm asking around. I like computer history, recreational math, and puzzles (and art, but I think the usual travel guides have got me covered there).