If it rains up in the Black Forest, the water reappears along part of this section over a km or maybe just over a couple of hundred metres only to seep away again when it stops raining. So it ends up in the North Sea instead of the Black Sea. An ongoing struggle between the Danube and the Rhine. After all, around 1900, the phenomenon could be observed for some 80 days a year. Visiting groups are provided with a guide.
Individual tours are also possible with the local tourist authority only too happy to assist.
The outcome was a biological zero zone. Then the flora and fauna gradually reappeared including rare birds and animals such as the European mud turtle, the peregrine falcon and unique orchids. As regional tourist director Uwe Kraus mentioned, there are caves in profusion throughout the Swabian Alb. Two of the most popular are at Erpfingen, a centre with a good mix of visitors for there is a lot to appeal to the older generation but also to families with young children as well as to teenagers, who can stay at the spacious youth hostel or on the camping grounds. The Bears' Cave gets it name from the bears which once lived there.