The Dingly Egg is an item appearing in the Fable II DLC See the Future. The egg is found on a skeleton after passing through the stone gates (which resemble the "Henges" of Stonehenge) in the swampy area of the Celestial Keep and is needed to open the entrance to Dingly Burrow. It is mentioned, along with the directions to unlock it, in the book The Grumpy Rabbit. The egg will disappear if you unlock it but do not collect it before you complete The Costume Party quest.