The mountain of Slieve Gullion is mentioned many many times in the ancient Irish battle epic, the Táin Bó Cuailnge, as Sliabh Cuilinn. There is a lake at the top of the mountain, known as the "Lake of Sorrow", or the Calliag Bheara's lake. There are two cairns either side of the lake.
The Chase of Slieve Cullinn. In which it is related how Finn's hair was changed in one day from the colour of gold to silvery grey.
Culand, the smith of the Dedannans, who lived at Slieve Cullinn, had two beautiful daughters, Milucra and Aina. They both loved Finn, and each sought him for her husband.
As they walked together one evening near Allen, they fell to talking of many things; and their conversation turning at last on their future husbands, Aina said she would never marry a man with grey hair.
When Milucra heard this, she resolved with herself that if she could not get Finn she would plan so he should not marry her sister Aina. So she departed immediately, and, turning her steps northwards, she summoned the Dedannans to meet her at Slieve Cullinn. Having brought them all together, she caused them to make a lake near the top of the mountain, and she breathed a druidical virtue on its waters, that all who bathed in it should become grey...
The little lake for which this legendary origin is assigned lies near the top of Slieve Gullion. There were several wells in Ireland which, according to the belief of old times, had the property of turning the hair grey. Giraldus Cambrensis tells us of such a well in Munster; and he states that he once saw a man who had washed a part of his head in this well, and that the part washed was white, while the rest was black!
It is to be observed that the peasantry of the district retain to this day a lingering belief in the power of the lake of Slieve Gullion to turn the hair grey.
We found that the natives of Dorsey hold to a belief in certain magical effects produced by the water of Lough Calliagh Beri. They would not tell us what would happen to anyone rash enough to bathe in it, but vaguely hinted that it would be something dreadful.