I think I might have mentioned that I worked at the Library of Congress this summer, down in the Preservation Directorate. The LC is made up of three buildings; I was working in the Madison Building, which was built the latest and is considered the ugliest of the three.
This is the oldest, and nicest building, the Jefferson. If you take a tour of the LC, this is the building you'll be touring, since it's really beautifully decorated. (Sadly, the tour does not let you actually read any of the books, but I think it's worth seeing anyway.)

Awesomely enough, the three buildings of the LC (Jefferson, Adams, Madison) are actually connected by an elaborate tunnel system. It makes getting lost a little easier, admittedly, but still. Tunnels! Tunnels are cool! You're walking dozens of feet underneath pavement and tourists and speeding cars, and they never know you're there!
Sightseeing aside, I <em>was</em> actually legitimately occupied this summer, working in Preservation. I'm going to have a lot of pictures in this explanation, so for the sake of your bandwidth (for those of you still using bandwidth) I'm going to put the entire explanation under a cut.