Altena is a small town in the wooded hills of the Sauerland, but it holds an outsized place in travel history: Burg Altena, the medieval castle above town, is where Richard Schirrmann opened the world's first youth hostel in 1914. The original hostel rooms have been preserved as a museum inside the castle, complete with period dormitories and Schirrmann's office, and the idea he started here grew into the global Hostelling International network with 4,000 hostels worldwide.
The castle itself is worth the visit beyond the hostel museum. It sits dramatically above the Lenne valley, reached either by a steep footpath or through a tunnel with an elevator carved into the hillside. Inside you will find a good regional history museum covering the area's wire-drawing industry. The separate Deutsches Drahtmuseum in the valley goes deeper into this story — Altena was once the wire capital of Germany, producing fine wire for piano strings, telegraphs, and surgical instruments exported around the world. The views from the battlements take in the forested hills that make the Sauerland a popular hiking region.
Altena is not a destination you would cross Germany for, but if you are in the area or have any interest in the history of budget travel, the birthplace of the youth hostel is a genuinely interesting stop.