Altensteig Castle probably dates back to the 12th century. In 1287, the castle was first mentioned as being owned by the Counts of Hohenberg. Hermann, son of Margrave Rudolf of Baden, conquered the town but had to return it to Count Burkhard von Hohenberg in 1288. In 1398, the Hohenbergers sold the Lordship of Altensteig to the Margraves of Baden. The castle became the seat of the Baden bailiffs.
In 1603, as part of a territorial exchange, Altensteig came under the rule of the Duchy of Württemberg. From 1605, Heinrich Schickhardt built the New Castle as the administrative and residential seat of the Württemberg bailiffs. The old castle served as a grain silo from the 18th century onwards. The lower part of the striking residential tower, with a floor area of about 11 meters by 16 meters, is made of sandstone masonry. The construction suggests that it was built in the 12th and 13th centuries. Presumably, an Alemannic timber-framed building was added to it in the 15th century. The six floors housed cellars, the great hall, kitchen, living quarters, and servant quarters. The largest room, now called the 'Knight's Hall,' is located on the second floor.
On the north side, the castle complex was protected by a wall with a battlement and two towers. The towers once served as a prison. While the western tower, called the 'Heaven' tower, had barred windows that looked out to the outside, the eastern tower, called the 'Hell' tower, had a 15-meter deep dungeon. The fortifications were connected to the city wall.
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.