The Clementinum in Prague is a historic complex of buildings that serves as the National Library of the Czech Republic. Its most famous feature is the Baroque Library Hall, completed in 1722. Known for its breathtaking ceiling frescoes by Jan Hiebl that depict motifs of science and art, the library has remained virtually untouched since the 18th century. It houses a collection of over 20,000 volumes, mostly foreign theological literature. A unique highlight is the collection of hand-painted globes and astronomical clocks crafted by the Jesuits. Legend says the Jesuits had only one book when they started building the library in 1622, but by the time it was finished, the collection had grown into one of the world's most significant. It is often cited as the most beautiful library in the world due to its perfectly preserved Baroque interior.