At the Skyscrapers level, go to the bottom of the crashed plane and to the left (if you were exiting the plane) is a small billboard. Shoot down the billboard and it will form a bridge between the gap of the two buildings. Place yourself in the center of the board and aim yourself toward the inner part of the hole. Depending on your vehicle, you will have to drive off at a different speed to get the black cube. Note: You will have to lose a life to get this black cube.