Rockin' Poncho mentioned the Seattle Public Library, the central library building, which reminded me that I meant to talk about it here - it's really really cool. It's also really really big, inspiring this list of ways to die in the new library, in The Stranger. There is more about it and a photo gallery here.
It's the only vertigo inducing library I know of. If you go all the way to the top and walk around behind the elevators you come to this sort of crows nest, a view to the main floor below (the yellow thing is an escalator):
