Contestants take an iron and an ironing board to the strangest and most extreme places they can think of, and do their ironing! For example: the top of a mountain, at the bottom of the sea, etc etc..

Amazed it is a sport, but it is. This crazy sport is an annual event held in England. A round of cheese is rolled down the hill and everyone taking part chases after it. The first person to the bottom wins the cheese. It’s not surprising to see multiple broken legs and other body parts due to the steepness and speed.
http://www.youtube.com/watch?v=ZC5ykhXDDbo

This is something I may actually try. Its where you get into an actual sphere like ball and roll around like a friggin' maniac :) Dig the video.

This is not something I would try but its amazing that anyone would attempt it, never mind 1000s who do it yearly.
http://www.freedive.net/freediving/freedving.htm