You scramble up the rocky face of a mountain that's among the tallest in the Rockies. If you slip, a climbing rope measuring just 3/8 to 1/2 inches (10 mm) in diameter is all that will prevent you from falling thousands of feet to the valley below. A gust of wind throws you off balance, but you're able to steady yourself, heart racing. You continue on, clinging to each rock with a white-knuckled grip.
Does this sound like a vacation to you? Such an adrenaline-pumping experience is one example of what the tourist industry calls adventure travel, which includes all kinds of activities, from bird-watching and horseback riding to climbing and kayaking. And it's becoming increasingly popular. According to a 2010 study conducted by the George Washington University School of Business, the Adventure Travel Trade Association and Xola Consulting, 26 percent of respondents said they'd participated in some sort of adventure travel, creating a global adventure market valued at $89 billion [source: GWU].
A small number of those surveyed -- just two percent -- had taken what's called a hard adventure trip. These vacations are higher risk and often require a great deal of specialized skill: Think trekking, climbing and caving. Today, tour operators all over the world cater to these thrill seekers in every way imaginable. Here are 10 examples.