The legend of Llyn Cwm Llwch
There is a fairy tale of an enchanted island invisible from the shore of the lake. A passageway leading from a rock to the island was said to be open on May Day each year. Those who had the courage to pass through the doorway would find themselves in a beautiful garden on the island inhabited by fairies.
The fairies would play enchanting music and tell stories of future events, and present visitors with flowers and fruit. Each guest was told nothing must be taken from the island.
One May Day a greedy visitor placed a flower he had been presented with in his pocket. When he emerged from the rock the flower vanished and he lost all his senses. Since that day the door to the island has never opened.