Anywhere in the game that you can manage to fall off the main game map, you will be teleported to the chicken experimentation room. Note: You cannot get out without restarting the XBox. Some ways to get into the room include:

Sweetsville factory
Unlock the low gravity cheat and jump on the roof of the building that holds the power switch. Jump off into the water behind it.

Prince Charming's Castle
Jump out of the window that you are supposed to kick the prisoners out of.