Olsztynek Castle was built by Ostródan Gunter von Hohenstein, the commander of Teutonic Order, between 1349 and 1366. The brick Gothic castle was conquered by Wladyslaw II Jagiello in 1410. It was destroyed in 1656 by Tatars of Crimean Khanate and left to decay. The castle was reconstructed in 1847-1849 and moved as a school.
References:Rosenborg Palace was built in the period 1606-34 as Christian IV’s summerhouse just outside the ramparts of Copenhagen. Christian IV was very fond of the palace and often stayed at the castle when he resided in Copenhagen, and it was here that he died in 1648. After his death, the palace passed to his son King Frederik III, who together with his queen, Sophie Amalie, carried out several types of modernisation.
The last king who used the place as a residence was Frederik IV, and around 1720, Rosenborg was abandoned in favor of Frederiksborg Palace.Through the 1700s, considerable art treasures were collected at Rosenborg Castle, among other things items from the estates of deceased royalty and from Christiansborg after the fire there in 1794.
Soon the idea of a museum arose, and that was realised in 1833, which is The Royal Danish Collection’s official year of establishment.