It is often possible to walk down the side of cliffs or mountains and return to the base. Where walking down is difficult or impossible, climbers rappel down their ropes or lower off.
To rappel, climbers thread their rope (or two ropes tied together) through an anchor point so that the ends hang below. The anchor might be a temporary setup using a rock or a tree, or it could be a fixed anchor; a common anchor consists of two bolts about a foot apart, a length of chain, and an attachment point.
Climbers use a rappel device (often the same as their belay device), through which the rope is fed and the device is clipped to the harness. With friction from the rappel device,it's possible to descend slowly and comfortably. Once all the climbers are on the ground, or at the next anchor, they pull one end ofthe rope until the other end clears the anchor above them and falls to their level. Then they can set up the next rappel, or, if they have reached the bottom, pack up for another climb.
Many modem climbs stop below the top of a cliff at a fixed anchor. Often, these climbs are less than half a rope length long, so the belayer can simply lower the leader to the ground. Then the belayer will take his turn on the route.
Although some people buy climbing equipment solely to go rappelling, most technical climbers view rappelling as a necessary evil. Because climbers often rappel when they are tired or the weather turns sour, and because it is one of the few times in climbing when one is depending solely on a few pieces of equipment, rappelling is when acddents are more likely to occur.