Altena is a town in North Rhine-Westphalia, Germany. It is in the Märkischer Kreis district. It is on the Lenne river valley It is in the northern parts the Sauerland. About 16,500 lived there in 2020. The major political party is the CDU. The Altena Castle is a famous tourist attraction in the town and is from the 12th century. There is also the Castle Holtbrinck, St. Matthew's Church, St. Katharine's Church and a special Holländer house. The main religious groups are Protestants and Catholics. During the German Refugee Crisis (2015/2016), Altena took in hundreds of immigrants and won the "National Integration Prize".