Great Journey Unused Objects
From Halopedia, the Halo Wiki
In the Halo 2 campaign level, The Great Journey, there are many unused objects that the developers put in and you can discover.
[edit] How To
You must have a Particle Beam Rifle for this to work. Proceed normally until you reach the part in which you have to escort Johnson's Scarab. Escort him until you can hijack a Spectre or Wraith.
When you have one, proceed to the area in which Johnson blows open the Control Room door and drives directly into the water. Head towards the island with the Control Room in it. When you reach that island, look for a sloping rock face. Climb it using the Spectre or Wraith, until you are above the water and on dry land. Continue to drive up the island using the boost and the hand brake, when necessary. Then go towards the highest point, either the top of the island's mountain, or the top of the Control Room. Both can be reached by simply boosting and hand braking to the top. When you reach the summit, or the top of the Control Room you can enjoy the view.
But there is also something else you can do. Get out the Beam Rifle. From your high vantage point it is easier to see this. Look to the right, then zoom in to x5. In x5 zoom search for something that looks out of place. When you find it in the sky, to the right of you, zoom in to x10. What you are seeing is the pillars from the levels High Charity and Gravemind. It is unknown why these pillars happen to be in this area, though it is speculated that they were meant to be incorporated in the final fight and left out. They can neither be reached, nor destroyed.
