Cologne Lowland

The Cologne Lowland, also called the Cologne Bay or, less commonly, the Cologne Bight (German: Kölner Bucht), is a densely populated area of Germany lying between the cities of Bonn, Aachen, and Düsseldorf/Neuss. It is situated in the southwest of the state of North Rhine-Westphalia and forms the natural southern conclusion of the Lower Rhenish lowlands and the transition to the Rhenish Massif (Rheinische Schiefergebirge or "Rhenish Slate Mountains"). The Cologne Bight is surrounded on the left bank of the Rhine by the High Fens and the Eifel, as well as by the Bergisches Land on the Rhine’s right bank. In the south and southeast the rising Rhine Massif, visible from far off by the silhouette of the Siebengebirge, form the conclusion of the bight at Königswinter. To the northwest the Cologne Bight opens out into the valleys of the Rhine and the Meuse, in the northeast it is bounded by the Münsterländer Kreidebecken (Münster Chalk Basin) of the Westphalian Bight.

The Cologne Lowland is among the warmest regions in Germany. While the summers on the upper Rhine are somewhat warmer, winters in the area are so mild that snow remaining on the ground for as much as several days would have been considered rather exceptional in the decades before the onset of the current climatic change. Due to the orographic rainfall on the surrounding mountain ranges the climate is relatively damp as well. In combination with the valuable loess soil, these factors make the Cologne Bight one of the most fertile regions of Germany.

...
Wikipedia