I would consider bungee jumping to be a good example of such an activity.You jump from a high place(perhaps a bridge or a hot-air balloon) 200 metres above the ground with an elastic(有弹性的) rope tied to your ankles.You fall at up to 150 kilometres an hour until the rope stops you from hitting the ground.It is said that 2 million people around the world have now tried bungee jumping.Other activities which most people would say are as risky(危险的；冒险的) as bungee jumping include jumping from tall buildings and diving into the sea from the top of high mountains.