Craig y Llyn towers above the lake, and it..
..had a green lady in the seventeenth century. Every seven years she came and sat on one of the rocks, making chains and necklaces of wild berries. The rowan or mountain-ash was her favourite tree, and she could be seen wandering about gathering an apronful of the bright red berries, which she conveyed to her favourite rock. Once when a man wished to follow her, but stood irresolute, she beckoned to him and smiled. He went towards her, and she gave him a handful of red rowan-berries.
He thanked her, and put them in his pocket. Then there came a crash, and the lady disappeared. She wore a green robe and green jewels. The berries changed to gold coins.
From chapter 15 of Mary Trevelyan’s ‘Folk lore and folk stories of Wales’ (1909). Online at V-Wales:
vwales.co.uk/Folklore/trevelyan/welshfolklore/chapt15.htm