Altena Castle was erected by the brothers Adolf and Everhard von Berg around the year 1108 after Henry V granted them land in Sauerland. On Wulfseck Mountain they built their castle, which they named Wulfeshagen, later Altena. This is one of the three legends of the establishment of the county of Altena and the building of the castle.
After the acquisition of Mark near the city of Hamm in 1198, the counts of Altena took Mark Castle as their primary residence and called themselves the Counts of the Mark. They occasionally inhabited Altena Castle and from 1392 onward it was used as a residence for the county bailiff (Amtmann).
In 1912, Richard Schirrmann established the world's first youth hostel within the castle, which is still in use today (Jugendherberge Burg Altena).
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.