The Klementinum library was voted as one of the most beautiful and majestic libraries in the world. The library which was first opened in 1722 as part of the Jesuit university having been a beautiful example of Baroque architecture. Just check it out.
Actually, the library houses over 20,000 book collections. And just look at its ceiling frescoes, they were painted by Jan Hiebl. But in 1781, director Karel Rafael Ungar established Biblioteca Nationalis, which can be called a collection of Czech language literature.
Due to the utmost importance of its book collection, some of the rare historical books have been sent to Google for scanning and will eventually be available on Google Books.
What is actually very little-known about this library besides its being rare and keeps treasure, which is very often associated with several little-known facts like, the Klementinum used to be the third largest Jesuit college in the world.