Altena is a town in North Rhine-Westphalia, Germany. It is located in the north of the Sauerland in the Lenne river valley, Population: 20,615 (2005). Area: 44.29 km². It belongs to the district Märkischer Kreis. Altena is twinned with Péronne in France (since 1967), Blackburn in England (since 1972) and Pinsk in Belarus (since 1990).
The town's biggest attraction is the castle Burg Altena. After being unused for centuries it was in ruins, although part of the buildings was used as a hospital. A complete reconstruction was undertaken, finished mostly by 1914, to celebrate the 300th anniversary in 1909 of the merging of Mark with Prussia (Brandenburg). In 1912 the first youth hostel was created by Richard Schirrmann inside the castle. The old rooms are still on display, and new rooms inside the castle area are still part of the hostel now. The dominant industry in Altena was wire production, and thus it has a museum dedicated to this industry only, the Drahtmuseum.