Burg Altena is a well-preserved medieval castle perched on a cliff above the Lenne valley, and it holds a double claim to fame: it is a genuine piece of 12th-century German castle architecture, and it is the birthplace of the world's first youth hostel. Richard Schirrmann, a teacher who believed that nature and travel were essential to education, established his first hostel in the castle in 1914, and the preserved rooms — dormitory-style sleeping areas, a common room, Schirrmann's office — are maintained as a museum of that original vision.
The castle also contains a well-organized regional history museum covering the Märkisches Sauerland's centuries as a centre of metalworking — wire-drawing in particular. Altena and the surrounding valley were once the wire capital of Germany, producing fine wire for everything from musical instruments to corsets, and the museum explains the industrial and social history of the craft with some excellent historical artefacts. Reaching the castle requires either a steep footpath through the forest or the Burgaufzug, a tunnel elevator carved into the cliff, which is the more interesting option.