The Ruhr is an industrial region of Germany located in the state of North Rhine-Westphalia. It is the largest urban area in Germany and one of the most densely populated areas in Europe. The Ruhr is home to many of Germany's largest cities, including Dortmund, Essen, Duisburg, Bochum, and Oberhausen. It is also known for its coal mining and steel production industries, which have been a major part of the region's economy since the 19th century.