Prague City Tourism, in cooperation with the National Library, operates a unique sightseeing tour on the premises of the Clementinum national cultural monument. The sightseeing tour includes an insight into the Baroque Library, the Meridian Hall and the Astronomical Tower. The Baroque library hall of the Clementinum is embellished with stunning frescoes with themes of the sciences and arts. The hall houses a collection of foreign language theological literature and several large, historically valuable globes. The library’s collection includes 27,000 volumes, mainly in the field of theology. In order to maintain a constant temperature and humidity, visitors are only allowed to look into the hall, not to enter it. The Meridian Hall is located on the second floor of the Astronomical Tower. This unique room was formerly used as a giant camera obscura, where a taut string was used to determine high noon. The walls of the Meridian Hall contain two original astronomical instruments called wall quadrants, used to measure the position of the stars. The 68 metre-high Astronomical Tower, which offers a magnificent view of the centre of Prague, houses an exhibition of historical measuring instruments and interesting facts about the tower’s history. The observation tower was originally used for astronomical observations from 1751, and it retained this function until 1938. Since 1752, it has also been associated with meteorological measurements, which became regular and systematic from 1775 onwards. For more than eighty years (1842-1928), high noon was announced to Prague citizens from this location.
