so i just figured out today that in testchamber 19 of portal, after going through a significant portion of it yourself, you were able to noclip to the cake room and to the aboveground place where it briefly shows after the credits.

screenshots are here, although most of you have probably already seen it.

http://www.xfire.com/screenshots/mistervengeance6/

and, please. if you haven't played portal yet, play it.