The Castle can be visited
Altena Castle

Altena Castle, a spur castle, is on a mountain spur of the Klusenberg in Altena in the Märkischer Kreis, North Rhine-Westphalia. It is also known as the site of the world's first permanent youth hostel.
History+
The construction of Altena Castle is, according to legend, attributed to the Counts of Berg, who are said to have received a piece of land from Emperor Henry V in the early 12th century. On the Wulfseck, they built a castle, initially called Wulfeshagen, and later named Altena. After acquiring the Oberhof Mark in 1198, the counts moved their main residence to Mark Castle and were henceforth called “Counts of the Mark.” Altena Castle served only as an official's residence from 1392. In 1367, Count Engelbert III of the Mark granted freedom rights to the settlement at the foot of the mountain. After a fire in 1455, the castle was only provisionally rebuilt and later served as a garrison. In 1771, it was sold to the city and housed a poorhouse and workhouse, as well as a criminal court with a prison. Reconstruction plans from 1834 failed due to financial difficulties. From 1856 to 1906, the Order of St. John used the buildings as a hospital.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.zeche.org/
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.2988, 7.6754