Llyn Gwernen is a lake by the side of the old road leading from Dolgellau to Llanegryn, at the foot of Cader Idris. A number of the farmers of Llanegryn were once hurrying home from a fair at Dolgellau (they were hungry, because the men who sold food at Dolgellau fairs in the olden time used to serve it up so hot that no one could touch it. The farmers were so busy that they could not wait for the dishes to cool, and so it was very little they had for their money). They saw a great man, with green water weeds entwined in his hair, and naked save for a girdle of green weeds, walking round the lake and crying in a querulous tone, "The hour is come but the man is not, the hour is come but the man is not," over and over again.
The farmers were frightened and ran home. Others also who returned home later than they saw and heard him, and it was afterwards found out that the great man with the green water weeds kept on complaining, The hour is come but the man is not," from ten o’clock at night until five o’clock in the morning.
Some days after, the body of an Englishman was found floating, swollen and horrible, on the surface of the lake. He had caused a great stir in the regions round about Cader Idris by sitting all night in the chair in which the astronomer Idris used, in early days, to watch the stars. (Idris was of more than ordinary stature. One day in walking he felt something in his shoe hurting him; he pulled it off and shook out three stones, which are still to be seen by the Lake of the Three Pebbles, Llyn y Tri Graienyn. One of them is twenty-four feet long, eighteen feet broad, and twelve feet high.) His object was to test the truth of the saying that anyone who spent a night in the chair would by morning be either mad, or a poet, or a corpse. So far from being a poet by the next day, he was not even a bard, and he certainly was not dead, then. It was therefore concluded that his intellect was deranged thereby, and he had in this state fallen into the clutches of the man with the green weeds, who had dragged him into the depths of the lake. The objection to that idea was that he must have been mad beforehand, because his chief delight was to climb to the summits of mountains. The folk who dwell at the feet of such mountains as Cader Idris and Snowdon make it a boast that they are much too sensible to attempt anything so silly.
From The Welsh Fairy Book, Jenkyn Thomas, 1907