Ask HN: What are the best (book) libraries in the world?

Every time I read about an excellent library in a particular U.S. or European city, I get a little jealous. It seems wonderful.<p>Does anyone know of a good clearinghouse or place to find information about libraries? Which ones are very friendly and pleasant for a foreigner visiting to come in and read there? Which ones have good digital collections? How hard they are to join?<p>Or even if they're restricted, it'd still be interesting to hear about.<p>It seems like it's all fragmented local knowledge. Share a bit about your favorite libraries?