I came across a series of youtube documentaries that follow the old routs on Britain’s oldest map, the Gogh map. In the sixth one it talks about the Arthurian sights. Glastonbury, Tintagel, Pendragon Castle and what sounds like the Wuthaler, a small, mystical lake.The lake is to the left of Pendragon hall and bear in mind the west of this map is what we would call north today.
I will give a signed copy of Shadow Over Avalon to the first person to come up with the exact map references of where this lake is today. Here is a big hint. It is in England.