Oulu castle ("Uleåborg") was built in 1590 for a stronghold to Swedish soldiers on their way to fight against Russian Karelia. The castle was mostly made of wood and earth walls. There probably was an earlier medieval castle on the same location. The Russian Sophia Chronicle has recorded that men from Novgorod tried to conquer a new castle in the Oulu River delta in 1377 but were unsuccessful. King of Sweden, Charles IX ordered to rebuild the castle in 1605. Old wooden parts were demolished and a new wall was built around the castle island.
Russians burned down wooden parts of the Oulu castle during the Great Northern War in 1715. Final destruction occured in 1793, when thunderstorm set the castle on fire and gunpowder magazine exploded.
Wooden constructions on the remaining powder magazine date from 1875 when the Oulu School of Sea Captains built their observatory on the site. The building has been a cafeteria since 1912 with a small exhibition on the castle history.
Varberg Fortress was built in 1287-1300 by count Jacob Nielsen as protection against his Danish king, who had declared him an outlaw after the murder of King Eric V of Denmark. Jacob had close connections with king Eric II of Norway and as a result got substantial Norwegian assistance with the construction. The fortress, as well as half the county, became Norwegian in 1305.
King Eric's grand daughter, Ingeborg Håkansdotter, inherited the area from her father, King Haakon V of Norway. She and her husband, Eric, Duke of Södermanland, established a semi-independent state out of their Norwegian, Swedish and Danish counties until the death of Erik. They spent considerable time at the fortress. Their son, King Magnus IV of Sweden (Magnus VII of Norway), spent much time at the fortress as well.
The fortress was augmented during the late 16th and early 17th century on order by King Christian IV of Denmark. However, after the Treaty of Brömsebro in 1645 the fortress became Swedish. It was used as a military installation until 1830 and as a prison from the end of the 17th Century until 1931.
It is currently used as a museum and bed and breakfast as well as private accommodation. The moat of the fortress is said to be inhabited by a small lake monster. In August 2006, a couple of witnesses claimed to have seen the monster emerge from the dark water and devour a duck. The creature is described as brown, hairless and with a 40 cm long tail.