From the BBC:

Zorb (Pic: www.zorb.ie)
The zorb protects the user with a cushion of air

Zorbing - effectively throwing yourself down a slope in a giant ball - has become the latest extreme sport craze to sweep the world.

Although zorbing was invented in 2000, it has only recently begun to take off around the world.

It involves a giant plastic ball, which has two skins - one inside the other. The person zorbing is in the area between the skins, which is pumped up with air. The middle ball effectively suspends them on a cushion of air 700mm off the ground, and the ball is then rolled down a hill.

"It's not really amazingly scary, it's not an amazing adrenaline rush - it's just bizarrely fun," the inventor of zorbing, Andrew Akers, told BBC World Service's Culture Shock programme. "I don't know why."

Like a number of other extreme sports, such as bungee jumping, zorbing originated in New Zealand.

Mr Akers explained that there are a number of reasons New Zealanders why have developed an attraction to developing these types of activities.

"We're so far away from anywhere that we've really had to make our own fun," he said.

(H/T to The Tyee)