Dortmund is one of the largest cities in the Ruhr Area. The city was founded in the 9th century and became in the 19th century one of Germany's coal, steel and beer centre. Completely destroyed during WWII, Dortmund shifted from being a heavy industry and mining city, to becoming a high-tech, cultural and educational centre. The old industries and mines were turned into museums, such as the Westphalian Industrial Museum or the Graf Wittekind Visitor's Mine. The city is also renowned for its parks and the Rosarium, a botanical garden with more than 2.600 varieties of roses. Dortmund also has many museums, like the Transport Museum and the Motor Car Museum, the Museum of Art and the Natural History Museum.