Play the old school free 4 all section. Note the building at the very end of the map on the opposite side of the bus. Get to the very top of the building that is around the corner. Do to so, first get to the second story where the chair is found. Get on the top of the chair facing the wall and jump. You may have to run and jump, but eventually you will catch an edge. You can then work your way up to the position. Once there, go to your right. Then, jump up onto the object just past the building that you are currently on. Walk around the building, trying to stay as close to it as possible. Then, look down. Make sure you are directly above the barbed wire. Follow that until you get to the building, then jump onto it. Then, just walk across to the other building. Note: You will be floating in air. When you get there, go to the extreme left of the building. Jump and you will notice a glitch -- you are on an invisible object. Once you get there, jump again to get on top of the building. Then, go backwards but do not go off the building. Run and jump just when you get to the front edge. You will now be floating in the air. When you are almost on the fence below, you will fall. When you fall, walk directly along with the fence or else you will fall. You can just crouch and shoot people.