2019 witnessed the discovery of a century for more than just the Bergisches Land: in Mühlenberg near Ründeroth, over the last 20 years researchers had searched high and low for an entrance to what they suspected was a cave, but once they found a way in to the Windloch they discovered an incredible underground realm of extraordinary crystals, limestone features and impressive caves of unimagined dimensions in which no humans had ever set foot before. Measurements taken in the first few months indicated that, at more than 8,000 metres long, the Windloch is the largest cave in North Rhine-Westphalia and one of the 10 largest anywhere in Germany. 

Ten information boards spread out along this roughly 8.4 kilometre route offer lots of detail about the work of the speleologists. You can also see sinkholes and karst springs, and can finally visit the Aggertal Caves as part of a guided tour. 

You can listen to the scientists report enthusiastically about their discoveries at two audio stations.