“Castel of the Dead”
The castle owned by Mabuz the Enchanter. It was surrounded by the river Der Kal (“River of Torment”).
The castle was enchanted in such a way that anyone who entered uninvited would turn into a coward; his cowardice, in fact, would be proportional to his prior courage. Lancelot happened upon the castle and succumbed to the spell, causing his companions – his lover Ade and his squire Tybalt – to desert him in disgust. Mabuz kept Lancelot prisoner for a time, but eventually freed him.
Source
Lanzelet | Ulrich von Zatzikhoven, c. 1200