The Regenstein Library at the University of Chicago. On my own list of the top five most beautiful ugly buildings in the world, it's number 3. It's a Skidmore, Owings, and Merrill building, completed in 1970. It stands on the former grounds of the great Stagg Field. (Think about that as a symbol of a university: Hutchins got rid of the football team in 1931 or something like that. Big controversial move. So build a library on the site--just to press the symbolic shift to academics--by 1935. Goodness knows, there were New Deal stimulus dollars around to do so, and Hutchins was a good fund-raiser. No**, get rid to the football program and then take 40 years to build on top of it.)
** Of course there are probably 100 stories about why this makes sense. And wasn't it under the stadium that the A-bomb research was first done?