Torre di Federico is an octagonal ancient tower that was allegedly a summer residence of Frederick II of Hohenstaufen. The two floors possess beautiful vaults. The aspect of the building is austere. It was part of a bigger complex, named Old castle and destroyed by Arabs. Remnants include some pieces of the old, imposing walls on the top of the green hill where the Tower rises.
The tower is an imposing 26 metres high, has a diameter of 17 metres and its walls are 3.5 metres thick.
The Clementinum is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic.
Its history dates from the existence of a chapel dedicated to Saint Clement in the 11th century. A Dominican monastery was founded in the medieval period, which was transformed in 1556 to a Jesuit college. In 1622 the Jesuits transferred the library of Charles University to the Klementinum, and the college was merged with the University in 1654. The Jesuits remained until 1773, when the Klementinum was established as an observatory, library, and university by the Empress Maria Theresa of Austria.