Twll Du

Literally "Black Hole".
On the circuit of Llyn Idwal, the path takes a demonic turn towards and in to "The Devils Kitchen".
I climbed it once, many years ago, and ended up with water running down my sleeve and out under my Blacks Ventile smock. (you have to be old to remember what a Blacks Ventile smock was.)
I still think its the hardest V-Diff I've ever done, it took all day and scared me off climbing for awhile.