Sometimes I have seen castles perched on top of ancient volcanic plugs where the hard rock precipitous rock has given the castle good defence. One such castle with extensive views across the countryside towards Bodensee (Lake Constance) and the Swiss Alps is Hohhentweil. It is one of the largest castle fortresses in Germany and has extensive casements and towers and massive cellars and until 1801 when it was largely destroyed by the French it must have been very impressive.