Zorbing. Globe-riding. Orbing. Zorbing. This is the sport of climbing into a clear, plastic ball (typically 10 feet in diameter), and rolling downhill at high speed. It looks like a giant hamster ball. Zorbing first hit the extreme-sport scene in New Zealand, and now it's available anywhere in the world. Usually, riders are strapped against one of the ball's walls. Not in hydro-zorbing, though. In that case, the operator adds about 5 gallons of water, and passengers slip and splash as the ball rolls.
Volcano-boarding. Adrenaline junkies: Head forth to Nicaragua. Prepare to zoom down a steep, 1,600-foot volcanic slope, on a plywood board reinforced with metal and Formica. One of the latest additions to the extreme-sport scene, it's only done on Cerro Negro, a charcoal-black active volcano that's erupted 23 times in the past 100 years. (The threat of another eruption always looms, though there hasn't been once since 1999.) Tourists pay $28 for the experience.