One of the staples for Ninja obstacles are the Unstable Bridges The low hanging wood or plexiglass planks dangle from sling hardware causing motion in all directions as soon as you step on them. The ninja must carefully scale across the plank while attempting to keep their weight distributed in the center of the board. Then comes the true test of leaping to board number two! The gap between the two bridges can be varied to increase or decrease the difficulty of the obstacle.