The Pillar of Autumn vacation

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 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.

link to the video through HBO