The Pillar of Autumn vacation
From Halopedia, the Halo wiki
Through a glitch, one can go through the glass of one of the airlocks of the UNSC Pillar of Autumn. After going through the hatchway by grouching and jumping you will fall. Upon reaching the invisible "floor" (a form of "invisible wall") you may loose some health. If it works correctly, you will be able to explore the underside of the Pillar of Autumn and Installation 04.
