Halo Vacation

In Halo 3, on the level "Halo", it is possible to escape from the regular map using the Elevator Glitch. Once you get to the part with the warthogs, drive until you see a big column, with verticle orange lines going across one side. Pull over there, and jump down into the smallhole there, and do the Elevator Glitch in either corner. ONce at the top, tehre will be a mass of things to explore.