Downhill mountain biking isn't a walk in the park. As you descend a mountaintop on a rugged mountain bike (with great shocks to absorb the bumps), you'll fly off rocks and encounter obstacles, combining fantastic scenery with serious thrills.
Mountain biking has its roots in a fascinating period of American history: In 1896, the U.S. Army organized an experimental regiment of soldiers, all African-American, who rode bikes instead of horses. Dubbed "buffalo soldiers," the men journeyed long stretches of difficult terrain on their bikes, laying the groundwork for modern-day mountain biking.
Once the U.S. made mountain biking a competition in the 1980s, the entire world was turned on to the idea of hitting the trails on two wheels. You can go it alone on many mountains that allow bikes, as well as specifically designed mountain-bike parks.
Where to go mountain biking: Sweden's Åre park is specially made for mountain-biking thrills, with 32 different trails to choose from, as well as chairs and a gondola to get you to the top.