This trick requires two playres. In online mode, go to the back of the map past the blown up building near the middle. There is a raised platform against the wall and a ladder on the side of here (it is the only place in the map with a ladder). Get two people to get to this ladder, then have one person go up the ladder as far as possible without drawing his weapon and looking straight up to the sky. Then, have the other person walk up the ladder below them, looking up. Say "go" or something else as soon as they hit the person above and keep going. As soon as the player on top hears this, he should go at the same time. This usually requires a few attempts. If done correctly, you will continue going past the ladder and into the sky. As soon as the sky turns completely white (because you should be looking up), move to the right until you fall. If done correctly, you will land on the roof of the building. Once here, you can jump onto the adjacent roof to the north, over the small wall. Once on this roof, slowly continue going down the roof. Once you reach the edge, you should be able to see some boxes below, like the little alcoves above the platform with the ladder. Aim for one of these and you should land in it. Once done, jump into the boxes on the other side one down each time. Gradually make your way down. Once you get to the floor, look to the east. You can clearly see a big "rip" in the map. Go straight down here and out the back of the map. Make sure you do not go out of the shadowed area or you will "fall off" the map and have to start all over again. When you have gotten out here, don't try and get into the map until you have followed this part: move south, without going past the shadowed area and without going near the buildings. When you get to the corner where the buildings stop, turn west and continue until you get to a turn in between some buildings. It is easy to see as there are lots of windows visible, and there is a gateway in the corner which should be to your north. Go down here, then go straight through the doorway. Once you have made it through, you can go absolutely anywhere under the map and shoot people or throw grenades at them, but they cannot see or shoot you. As long as you do not go out of the shadowed area and do not waste ammunition, you can continue to play down there.