The castle of Virtsu belonged to vassals of the feudal state Bishopric of Ösel-Wiek - Western part of nowadays Estonia as well as part of Saaremaa and part of Hiiumaa. It was built in 1430 by Uexküll noble family and destroyed already in 16th century. Now the ruined walls are few metres high, but it really looks that there is almost nothing. That's because grass and bush is growing on the ruins.
Reference: Virtual Tourist
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.