Devil's Wall is a rock formation made of hard sandstones from the Upper Cretaceous period in the northern part of Kassel, Germany, and is one of the oldest nature reserves in the country. The monument or wall is about 20 kilometers long and contains a number of towering rocks. Here, as you stroll through the area, you can see many plants that have become rare and that have grown among the crevices of the rock. Colorful flowering herbs such as mountain sand bells, sandy thyme and carnations find a good habitat here.