One of my students suggested we make a zip line.  We started with the suspension bridge, using only one of the towers. We attached the 2 main cables to the lower rung of a ladder about 10 feet away.  The deck, which is now  the trolley, hangs from the 2 lines just like it did when it was the deck of the suspension bridge.

Then we decided to make it more functional by adding a hoist. We attached a windlass to the tower and ran a line down to the trolley. Now we could haul the trolley up the zip lines, and the weight of the trolley would slide it down the lines.    

       Now for the hoist. We added a sheave ( white plastic pulley wheel) to a dowel inserted into the middle of the trolley, and ran this line (with a hook at the end) up over another sheave on top of the tower and then under yet another sheave  near the base of the tower.