The creatures of Celtic Mythology are extremely interesting and give us a real insight in to the collective psyche of the time.
Often, these creatures were a way for the Celts to explain the world around them, or served some purpose.
For example, in Scottish folklore it was said that a Big Grey Man lived atop Ben Macdhui. This physical phenomenon (usually known in modern times as a Brocken Spectre) is caused by the low sun casting a shadow on to a bank of fog or cloud.
Many stories end in tragedy or misfortune, and serve as a warning or lesson.