Whitehorn Memorial Library, VictoriaCity Caledon (59,196,23)
With art galleries on several floors and an extensive collection of books on the Third Floor, I'd say this main Library in Caledon VictoriaCity is the best library in SL. Of course, I am a bit prejudiced to the 19th Century and steampunk (grin).

The Third Floor has steam-powered Card Catalog machines: chests and chests full of books delivered to you at the touch of a button!

A fabulous place to explore, read and relax. See if you can figure out what the giant Tesla device built into the roof does!

If you want to show anyone an excellent example of what a Library can be in SL, show them the Whitehorn Memorial Library in Caledon VictoriaCity!