Altena
| Altena  | |
|---|---|
| View of Altena Castle in September 2008 | |
| Location of Altena  within Märkischer Kreis   district | |
| Coordinates: 51°18′N 07°40′E / 51.300°N 7.667°E | |
| Country | Germany | 
| State | North Rhine-Westphalia | 
| Admin. region | Arnsberg | 
| District | Märkischer Kreis | 
| Subdivisions | 7 | 
| Government | |
| • Mayor (2020–25) | Uwe Kober (CDU) | 
| Area | |
|  • Total | 44.29 km2 (17.10 sq mi) | 
| Highest elevation | 511 m (1,677 ft) | 
| Lowest elevation | 145 m (476 ft) | 
| Population  (2023-12-31) | |
|  • Total | 16,657 | 
| • Density | 380/km2 (970/sq mi) | 
| Time zone | UTC+01:00 (CET) | 
| • Summer (DST) | UTC+02:00 (CEST) | 
| Postal codes | 58741–58762 | 
| Dialling codes | 02352 | 
| Vehicle registration | MK | 
| Website | www.altena.de | 
Altena (ⓘ; Westphalian: Altenoa) is a town in the district of Märkischer Kreis, North Rhine-Westphalia, Germany. The town's castle is the origin for the later Dukes of Berg. Altena is situated on the Lenne river valley, in the northern stretches of the Sauerland.