Or “Hollow of the Shannon”. This is Tony after he had been diving there.
The pool is the legendary source of the river Shannon. According to Wikipedia, the Shannon is named after Sionnan, who was the granddaughter of Manannán mac Lir, the god of the sea. She came to this spot to eat the forbidden fruit of the Tree of Knowledge, which was planted by the druids. As she began to eat it, the waters of the pool sprang up and overwhelmed her. She was drawn down into the pool and its water began to flow over the land, forming the River Shannon.
The resurgence has been dived most recently by Al Kennedy, Paul Doig, and Artur Kozłowski.