This can only be used in Free Play mode.

When you're in The garage part in the Shanghai Showdown, jump up to where the box is and then push it. it will explode.

Then you can build a hatch.

Then, get a small character and press B to enter it.

After you get up change to a girl character (use the triggers to change characters) and then go to the top and onto the tiny platform.

When you see that little thing with the bars and stuff in front of you, jump to it and walk the way where it faces out.

In a split second you are walking on air.

Have fun - this cheat is cool, you can access the little areas where you can't usually go and the background is black with a city-like feature.