You have entered another dimension.  It is a dimension not only of sight and sound but of mind.  A place of things and ideas.  Between the pit of Man's fears, and the summit of his knowledge.  You have entered:  The Minus World.

Seriously, I was thinking some cheats and/or secrets in games are truly bizarre.  Or so obscure that you wonder if someone actually discovered it or the developers leaked it.  

Like the minus world.  For those of you who are unfamiliar with this "secret" (read: glitch) here you go:

 Super Mario Bros.-  Go to World 1-2. At the pipe that leads to the flag, break two blocks so there's one at the end touching the pipe. Now duck and jump backward toward the brick (don't break it!). You should go through the wall and pipe into a warp zone. Jump down the first pipe you see and you will be in the Minus World (-1)! 

Name your favorite bizarre and obscure cheats and secrets! 

well how about the black hole glitch in SSBM

In Resident Evil 2 you can click on a trashcan in the S.T.A.R.S office 100 times and recieve a dull "nothing's there" message every time until the 100th, when you'll suddenly find a couple of grainy and ultimately useless photos...

The "Sommersault" cheat from Age of Empires also springs to mind; you type it in and your catapults start using workers for ammo, and they do a flip midair while saying something completely incoherent. (I think I'd be rather incoherent as well were I flung with a catapult... )

 I've never heard of that one, care to elaborate?

In Metroid Fusion there's secret message you can see, but only by skipping an upgrade and performing some spectacular acrobatics. This is one I think had to have been leaked by the developers.

http://mdb.classicgaming.gamespy.com/index.php?g=m4&p=tips#navroom

 http://youtube.com/watch?v=G28w008jeHg

the 3rd time they succeed 

 Hah that's awsome.  Definitely makes you wonder how anyone figured that out.

Super Metroid's "Murder Beam" glitch is pretty odd. As is the reset glitch, that returns all environment switches back to their original state without actually rebooting the game (meaning you can re-grab everything and re-watch all events).

The Pokemon missingo glitch, that was weird but very sweet. Also glitch city Pokemon glitch too.