In Antarctica in winter, the temperature can get to minus 100 degrees Fahrenheit at the geographic South Pole. It's a lonely place to live and societal interactions allow the ones who "over-winter" a bit of respite. With a well-built sauna, the people could get the inside temperature up to 200 degrees Fahrenheit. Once properly warmed, a burst outside would expose them to a temperature difference of 300 degrees Fahrenheit. Since the name is based on Fahrenheit, the Celsius equivalent temperatures are insignificant.

For those who want a different club, it would be the 166 and 2/3 Club in Celsius. The sauna is at 93 and 1/3° and the outside air temp is at -73 and 1/3°

To become a member of the Three Hundred Club, the participant first warms up in the 200°F sauna for a bit. Then the participant runs around the geographic South Pole, naked, and gets back into the sauna to warm back up.

Being a member of this club and having accomplished the feat in Antarctica is a dubious honor, but allows one to wear a custom-made patch denoting membership.

Somewhat recent changes to the rules allow the participants to wear flip-flop sandals to prevent foot frostbite.

More Info: en.wikipedia.org