Zorb
Was looking at New Zealand tourism sites last night and came across the Zorb site. Put a person-sized transparent plastic ball inside a bigger transparent plastic ball, with the space between filled with air. Now put a person in the inner ball:
He's got about 700 mm of air between him and the ground and this air cushion keeps him safe as he hurtles down the side of a hill at speeds of up to 50 kilometres per hour. ...[As] the ball rolls around, the person ... becomes pinned to the inside, just like water inside a bucket being spun around your head.
(Quote from the Zorb: Rotorua Adventure page.)
Apparently Peter Gabriel used one of these in a recent concert tour. Presumably without the hurtling down a hill part.