From P. W. Joyce’s Origin and History of Irish Names of Places (Dublin: McGlashan and Gill, 1869):

In the parish of Kilgobban in Kerry, about eight miles west of Tralee, is situated the beautiful valley of Glannagalt; and it was believed not only in Kerry, but over the whole of Ireland, wherever the glen was known, that all lunatics, no matter in what part of the country, would ultimately, if left to themselves, find their way to this glen to be cured. Hence the name, Gleann-na-nGealt, the valley of the lunatics. There are two wells in the glen, called Tobernagalt, the lunatics’ well, to which the madmen direct their way, crossing the little stream that flows through the valley, at a spot called Ahagaltaun, the madman’s ford, and passing by Cloghnagalt, the standing stone of the lunatics; and they drink of the healing waters, and eat some of the tresses that grow on the margin—the water and the cress, and the secret virtue of the valley, will restore the poor wanderers to sanity.

The belief that gave origin to these strange pilgrimages, whatever may have been its source, is of great antiquity. In the ancient Fenian tale called Cad Finntragha, or “The battle of Ventry,” we are told that Dairif Dornmhar, “The monarch of the world,” landed at Ventry to subjugate Erin, the only country yet unconquered; and Finn-mac-Cumhail and his warriors marched southwards to oppose him. Then began a series of combats, which lasted for a year and a day, and Erin was successfully defended against the invaders. In one of these conflicts, Gall, the son of the king of Ulster, a youth of fifteen, who had come to Finn’s assistance, “having entered the battle with extreme eagerness, his excitement soon increased to absolute frenzy, and after having performed astounding deeds of valour, he fled in a state of derangement from the scene of slaughter, and never stopped till he plunged into the wild seclusion of this valley.” (O’Curry, Lect., p. 315.) O’Curry seems to say that Gall was the first lunatic who went there, and that the custom originated with him.

From the Irish Times, October 23, 2012:

The scientific analysis carried out on behalf of the TG4 documentary confirms the presence of lithium in the well water, perhaps going some way towards explaining the link between the well and people with mental health issues through the centuries.

One of those who has visited the well in recent times is Dingle-based writer Dairena Ní Chinnéide (43), who was diagnosed with bi-polar disorder almost two decades ago. Ní Chinnéide grew up near a well and her father instilled in her some of the traditions about wells and rural life.

“I liked the water and I felt there was something very cleansing to it. At times when I felt very low, I would visit it and it gave me peace of mind.” (source)

Image: View of Castlegregory and the Maharees from Gleann na nGealt (source)