In this glitch you can either spawn on the right or left.
Next go to the tourque bow (but you do not have to pick it up).
Then attach to the wall where you can see the people where they have spawned, and run while in cover back and forth, if done correctly you will get on top of the legde (do this glitch when the train is going by so you dont get killed by the tourque bow or people on the other side).
Now keep walking on the ledge until you see a giant area of blackness or a black hole.
To get there, there should be poles on the egdes, go up to one and do a roll.
If done correctly you should fall off the ledge and go into the black hole.
You can do anything you want here, but you will die after a while.
Very rarely if you fall in the black hole you sometimes end up in the basement where the grenades are.