Why do we seek out the gnarliest singletrack, the murkiest whitewater, and the steepest ski runs? Why don't we just sit on the beach and watch the waves roll in rather than surf them? It's called the element of danger, and it's what pumps up our adrenaline and makes the finish line so sweet. While it's impossible to totally eliminate danger from any outdoor pursuit, good fitness, prudent planning, and a little bit of skill can minimize it. But there are a few trips out there where danger—and even death—are a serious possibility. Here are some of the U.S. and Canada's riskiest adventures, and our strategies for surviving them.