When this work was finished, and the masons and carpenters had left. Merlin said to the maiden, “Now this dwelling is worth nothing to you unless I make it so well hidden that no one can see it but those who live in it.” Then he began to work his spell, and he closed in the house on all sides so marvelously that nothing was visible but water. If you were outside, however much you looked, you would see nothing but the lake.

When he had worked his magic, he showed it to the maiden and said to her, “Is your house well hidden? Nobody who comes this way will ever see it, nor will he make it out, however close he gets, unless he is of the household itself. And if any member of your following wants to make it known to others, either through envy or through hatred, he will instantly fall in the lake and perish.”

Post-Vulgate Merlin