This section is from the book "Ancient Legends, Mystic Charms, And Superstitions Of Ireland", by Jane Francesca Wilde. Also available from Amazon: Ancient Legends, Mystic Charms, And Superstitions Of Ireland.
It is related of St Kevin that after he had been seven years at Glendalough, a weariness of life came over him, and a longing to hear the voice of man once more. Then Satan came to him in the form of an angel, bright and beautiful, and persuaded him that he should quit the valley and travel abroad and see the world, while yet his youth was left to him. And St. Kevin was near yielding to the words of the tempter, when fortunately St. Munna came by that way, and he at once saw through the trick, and showed to St. Kevin that the advice was from the devil, and not from God. And St. Kevin promised St Munna that he would never leave the valley till his death. However, God, not wishing that the saint should eat his heart away in idleness, bade him build a monastery on the east of the lake, the place where the resurrection was to be ; and he sent his angel to show him the exact spot.
But St. Kevin, when he saw the place so wild and rude, could not help telling the friendly angel that it was very rugged and difficult to build on ; and the stones were heavy and hard to be moved. Then the angel, to prevent any difficulty in the building, rendered the stones light and easy to move, and so the work of building went on to the glory of God ; and St. Kevin rejoiced in the task set before him.
And the monk who tells the story adds, that from that day in all the place which the angel appointed for the building, there is now no stone that cannot be lightly moved and easily worked all through the valley of Glendalough.