Because I am a book dork, I am completely fascinated by the New York Public Library, most especially the Main Library on 5th/42nd. I love the fact that the stacks of books at the main library run all beneath Bryant Park. I love the pneumatic tube system that whisks away the paper with your book request, issues you a number, which you then exchange when your books show up about 10 minutes later on the other side of the desks. I love the main reading room, where I sometimes have gone to do some half-baked research, just so I can sit in that cavernous, hallowed room with the wood tables and green-shaded lamps. I love the two lions, Patience and Fortitude that sit guard on 5th Avenue. The historical exhibits they have upstairs are always book and paper based, and incredibly interesting. And I don't really like Ghostbusters, but I even like the fact that some it was filmed there.
A tour is available of the stacks one time a year with a $40 contribution as a "Friend of the Library". See some pix of the miles of stacks beneath the park here.