Heres a nifty glitch that enables yout to get out of Halo 3's map Valhalla
Here's a short tutorial:
1) Go to the base with the water behind it.
2) If you are looking out at the water, go to the left until you cant go any farther because of the rock wall.
3) Now you should two rocks in the water. Jump on the bigger rock's edge so you stay on and keep holding forward(you WILL slide off, dont worry, just keep trying).
4) Now Keep going forward until you are in the crack of the rock and wall.
5) Crouch and move forward and you are out of the map, do not fall off the edge underwater or you will die.
6) You can also go all the way to the other end and grenade jump in between the big rock and the mountain edge, but you really can do anything else.
