Blackhammer Chambered Cairn is a Neolithic cairn on Rousay. It is thought to date from around 3000 BC. The structure is a typical stalled cairn, with an interior divided into seven compartments by pairs of upright stone slabs. The cairn has a modern roof, as the cairn originally was only a few feet high. Access is by a hatchway and ladder in the roof, as the original entrance was sealed. There have been finds of bones and pottery in the cairn.
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.