Underground mining tunnels and shafts pervade the Ruhr region and can reach depths of up to 1,300 meters. Large amounts of coal and stone were transported to the surface over time. As a result, hills formed in many places across the otherwise flat landscape. However, the material is not present underground. Shafts collapsed frequently, causing landslides, house cracks, and hollow spaces known as "Tagbrüche," or "day breaks."

In Bochum, a 500-square-meter crater suddenly caved in one Sunday morning. Luckily only two garages collapsed, and no people were hurt. In some places, the land is slowly sinking. The city of Essen, for example, has sunk 20 meters in the last 100 years. As the earth's surface sinks deeper, the groundwater rises. Large parts of Essen would be a lake by now if water were not pumped out day and night. Similar water pumps are operated throughout the Ruhr region. Every year, they transfer around 900 million cubic meters of water into rivers like the Rhine and Ruhr. These delayed effects of mining are expensive. Pumping out the water, damage to houses and the like cost approximately €200 million a year. And there is no end in sight.