Interesting/Important Fictional Libraries

Derry Public Library, from It

Yuriatin Public Library, from Doctor Zhivago

Library of Books Never Written, from The Sandman

That’s all I can think of at the moment.  I know second-hand of some others, in Eco for instance, but I’m not listing them until I’ve read the respective books.  This list will hopefully grow longer.  Kind of sad at the moment.

UPDATE:

Forgot a couple of fairly obvious (and similar) ones-

Hogwarts Library, from Harry Potter

Unseen University Library, from Discworld