This story actually applies to the next hill but despite being called a ‘Dun’, it’s not marked on Canmore’s map as such. Clauchlands, or Dun Fionn, is marked as a vitrified fort. It might be advisable to take your darning needle with you on an expedition to either.
A hill at Corriegills, called Dundubh (Black Mount), was said to have a cave in which the fairies lived, and this cave was full of treasure. To this home of the fairies an old man called Fullarton would betake himself, as often as he felt inclined. He frequently took a stocking with him and sat knitting and talking with the fairies. But the fairies were not always inclined to let any one away if they could detain him. Fullarton was aware of this fact, and always placed a darning needle in the collar of his jacket, or took a piece of rowan with him; when these precautions were taken by a person, the fairies had no power over them. On one occasion, however, he had omitted to take either of these objects, with the result that the cave nearly closed before he could escape.
From The Book of Arran, volume 2, by W.M. Mackenzie (1914), page 269.