Another story connected to the site:
“This,” said the narrator, [being a story about Gitto Bach] “made me more anxious than ever to see the fairies,” and his wish was gratified by a gipsy, who directed him to find a four-leaved clover, and put it with nine grains of wheat on the leaf of a book which she gave him. She then desired him to meet her next night by moonlight on the top of Craig y Dinis. She there washed his eyes with the contents of a phial which she had, and he instantly saw thousands of fairies, all in white, dancing to the sounds of numerous harps. They then placed themselves on the edge of the hill, and sitting down and putting their hands round their knees, they tumbled down one after another, rolling head-over-heels till they disappeared in the valley.
The next anecdote is told by another person present, about the Vale of Neath, so I feel sure this is the right Craig y Ddinas. From ‘The Fairy Mythology’ by Thomas Keightley
[1870], on line at the sacred texts archive.
sacred-texts.com/neu/celt/tfm/tfm163.htm
[to be replaced with the source]