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In many cities, it is common to find two buildings separated by only a narrow alley. The ideal distance would be a little greater than the distance between your elbows when you extent both of your arms out to the side. Your left hand and foot will go to one wall, while your right hand and foot will go to the other. Apply pressure to both walls simultaneously in order to hold up your body's weight. As you do so, you will have to increase the pressure you apply with the other hand or foot that is on that particular wall.
Find two walls that are close together. Place the hand and foot of each side of your body onto one wall. Move one hand or foot up at a time.