In 1264, castrum Hackenberg is mentioned as a site for document sealing. After the last Hackenberger died, the property passed to Alber Stuchs von Trautmannsdorf in 1382. Christoph Kuenritz bought and converted it into a Renaissance castle in 1543. Plundered in 1620 during the Thirty Years' War, it remained devastated until Sigmund Friedrich von Sinzendorf purchased it in 1650. His nephew, Theodor Reichsgraf von Sinzendorf, remodeled it into a Baroque palace between 1679 and 1677. After Prosper von Sinzendorf's death in 1822, it passed to the Reuß-Köstritz princes but fell into disrepair.
In 1945, it came under Soviet administration as German property, and in 1955, it was returned to Prince Reuß. Artists from the Vienna Group, including Friedensreich Hundertwasser, moved in from 1959. Captain Josef Steiger bought it in 1974, and in 1986, Horst Wächter, Hundertwasser's former assistant, acquired it. The Osmann family took over in 2020, with Horst Wächter remaining for historical research.
The four-story structure features Renaissance geometry and proportions, with medieval foundations. A cosmological mysticism, likely embedded during the 1679 Baroque renovation, is present. The four wings align precisely with the cardinal directions, enclosing a rectangular courtyard. The southern wings retain colorful ceiling frescoes and stucco decorations.
Access is via a short alley in the northeast, crossing a stone bridge into a frescoed entrance hall, leading through the courtyard with an octagonal fountain to a three-bay shell grotto, the 'sala terrena,' decorated with statues, frescoes, shells, and stucco, extending into the garden. The former access extended over the moat to a landscaped area with a Baroque-era artificial lake.
The Initiative Hagenberg association hosts cultural events at the castle.
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.