The Ruhr Area (German Ruhrgebiet) is an urban agglomeration in western Germany, in the state of North Rhine Westphalia. It is one of the largest urban agglomerations in Europe, even though not a single city in it reaches anywhere near a million inhabitants. However, in its wider definition, as the Rhine-Ruhr Metropolitan Area it includes Cologne, which does have nearly a million inhabitants. On the other hand, even though it contains so many cities, it is a smaller metropolitan area than London, Paris or Moscow.
The area's coal reserves, and its subsequent heavy industrialization spelled trouble, and it hence is significant in history and alternate history alike: including for example the occupation by the French in the aftermath of WWI, or being the prime target for the infamous Morgenthau Plan.
Due to its overt similarity with the Sprawl from William Gibson's Neuromancer trilogy, the Ruhr Area was also prominently featured in German Cyberpunk fiction, for example in the Shadowrun franchise/universe.