This egg is on the level "The Covenant." At the beginning of the level, when you destroy the AA wraith and get the new warthog, drive to the place where the wraith, ghosts and prowlers are. Where the shade turret is, grenade jump onto the ledge nearby. Then go up until the invisible barrier blocks your way. Jump off and you should be levatating. "Levatate" to the cliff next to you and walk up it. Then go off the edge of the cliff and the sky will turn orange, and you will be at the part where you have to fight the two scarabs, although there will be no scarabs, banshees or hornets. You sould be JUST outside of the map. Continue on until a mysterious structure appears. It will look normal at first, but look at the back of it! It is covered in blue letters on a grid-like multi-colored backround.

Enjoy ;)