Bungee jumping involves leaping from a great height while attached to a long elastic cord. The jump is usually from a tall structure, which may be a building, crane or bridge. Generally, the jumping platform is a fixed object but the activity can also be performed from a movable platform like helicopter or hot air balloon. When you jump from the platform, the elastic string tied to your body stretches downwards, and when it recoils, you are pulled upwards.