A must for its immense collection and three unusual museums.
Many say the world's most beautiful library.
With more than seven million items, not only is this one of the world's most important and comprehensive library collections, but the Baroque-style structure that houses it has come to be considered by many the world's most beautiful library. It was built during the 17th-century reign of Charles V, and has as its interior centrepiece the so-called Imperial Salon, more than 70 metres (230 feet) wide, filled with marble statuary, works of celebrated international painters, and more than 200,000 books. Also contained within is the Globe Museum, full of globes and items relating to the study of celestial bodies; the Museum of Papyrus, with examples dating back to 2,000 BC; and the Esperanto Museum, which lays out the vicissitudes of history of not only this language but other invented languages (even Klingon!).