We were camping in the Lesse river valley region and the farmer feared that his cow had fallen into a hole. Throughout the centuries the limestone ground under these Belgian campsites has been eroded in many places, creating enormous underground areas. With every rainfall the water goes through tiny cracks in the limestone, where the carbonic acid (which is always there in the rain) makes the limestone dissolve slowly. When the hole gets deeper, a creek or river takes over the grinding and this goes on like a cycle. Just see what happened near the Belgian campsites of the village of Han. The Lesse left its original bedding for a subway and after centuries of stone polishing became an underground river. The result is the famous Han cave complex. The water has created a number of caves like the “Koepelzaal” (Dome hall) which measures 62 metres in height and over 125.000 m2 volume making it one of the largest in Europe. The river travels through the caves, and resurfaces a kilometre further next to our Belgian campsite . Europe has plenty of caves, but the Walloon part of Belgium has a lot in particular.