St. Nicholas' Cathedral is a significant, well preserved example of northern German Late Brick Gothic; the church features three aisles, two transepts and a single-aisled ambulatory. Particularly impressive is the church's northern tiered gable. The church features 22 stained glass features considered to be treasures of international significance, a feature of the cathedral elevating the building to a heritage site of Europe-wide importance.
The cathedral was founded in 1188 by Margrave Otto II. The construction of present building was begun in 1423. In World War II the cathedral suffered damages during an air raid on April 8, 1945. The vault of the south transept and parts of the cloister were destroyed. The medieval windows had been removed before and survived.
References: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.