Rheinisches Braunkohlerevier
The Rheinisches Braunkohlerevier, often called the Rhenish mining area, is a lignite mining area or district in the Cologne Bay, on the northwestern edge of the Rhenish Slate Mountains. The mining of lignite using the open pit method has had a significant impact on the landscape here and led to the formation of several important industrial sites.
Source: Wikipedia — Rheinisches Braunkohlerevier (CC BY-SA 4.0)