I went to get my library card today and was pleasantly surprised by the sight of this beautiful building. You guessed it, designed by Mies van der Rohe. Wikipedia says that not only is it the only Mies building in Washington DC, but it also was his last project and only library. The librarian I was talking to said the staff was surprised recently when they found out the building was a historical landmark and couldn't be replaced. I informed the librarian that the Barcelona chairs in the reading area were also designed by him.
Check it out if you're in town.