Multiple areas to explore using a simple strafe jump
1. Make your way up to the cannon and hop on the rails located up the stairs opposite side of the bomb location
2. Jump towards the back side of the stairwell area and from here there are multiple locations to jump to !!!
Here is a glitch for the very first room in the game (spawn room) it's a definite glitch that i would recommend you thrash before it gets patched. You will be invincible, with unlimited ammo and zombies will pile up in front of you.
Before you start the glitch you'll need a friend...