Trinity College Library (the 'Long Room'), Dublin. There has been a library at the College ever since it was founded (in but the Long Room was not begun until Completed in it is the largest library in Ireland, containing books.
Book Nook in a fireplace that is no longer usable. Very creative use of space. Just make sure to clean that fireplace well before putting any books in there and to seal things to prevent water damage or pests from coming down the chimney.