Fall through blackness
Get to Part 2 Chapter 2 Continued..., when you get to the suspended walkway on the fourth floor where you first see the commandos. When you shoot the red crates they will blow up the walk so that it forms a ramp to the walkway below. Try to get under the falling piece of walkway so that you are holding it up with your head. Once you are in that position, kill yourself with a Molotov Cocktail or a grenade. When you die, you will fall through all the walkways and finally the ground floor. You will then fall through blackness. Note: Save your game before attempting this glitch.