The Sewers of Dross
The Forlorn Hollow
The 7 Planes of Hehenna
Warp Zones

If I get enough clicks on the google ads, I'll be much more likely to complete this website.

Konami Code

In keeping with their old-school side-scroller theme, Chronic Logic included a variation of the famous Konami Code (like on the Nintendo game Contra).

You can press:

[UP] [UP] [DOWN] [DOWN] [LEFT] [RIGHT] [LEFT] [RIGHT] A [SPACE]

... at the "Chronic Logic Presents..." splash screen to activate Turbo Mode.  This makes everything faster, but not unmanageably so.  It can help you speed through the game a bit.  I don't think there's a way to turn it off without exiting the game, though.

Super Size

From the Credits menu, if you type "supersizeme" you will hear a splatting/crunching noise.  Start playing, and Gish will be...well...radially enhanced.  In other words, fat.