In the winter of 1807, a lone fur-trapper journeyed deep into the heart of the Rocky Mountains. Somewhere near the headwaters of the Yellowstone River he found a lost world. A wonderland, ruled by ice, fire and brimstone. A world of extremes that challenges all that strive to live here. A place that has become perhaps the most treasured wilderness on Earth. Winter in Yellowstone. Minus 40 degrees. Fahrenheit or centigrade, it doesn't really matter, at minus 40 the two scales read the same. For half the year, Yellowstone is frozen solid. Yet in the middle of this ice world there is scalding heat. This is no ordinary place and this is no ordinary winter. The fate of everything here lies in the hands of forces of almost unimaginable power. Yellowstone is deep in the heart of the Rocky Mountains of North America. An isolated high plateau defended by rugged peaks. And its location is what makes it so different. Right beneath Yellowstone a unique quirk of geology means that molten rock from deep in the earth comes unusually close to the frozen surface. No one knows why it happens right here, but its impact is what has made Yellowstone world famous. Yellowstone is the most extensive geothermal area on Earth. It has over 10,000 thermal wonders and more geysers than the rest of the world put together. Old Faithful is Yellowstone's most well-known geyser. It shoots 5,000 gallons of water 150 feet into the air almost every hour.