Climbing at high altitude can be nauseating, dizzying, and it can kill you. It's cold up there, and let's face it, humans have evolved to live in relatively warm climates. If had we had evolved to live in constant cold, our bodies might have grown thick hair all over, we might store more fat, and our body shape might be rounder and shorter to prevent heat loss. In addition, Denali is the highest mountain in North America. And the higher you climb, the thinner the air is and the harder it is to breathe.

Weather on Denali can be severe—with whiteout snowstorms and winds at 100+ mph. Temperatures can feel as frigid as -100°F. The ability to recognize and treat cold and altitude injuries can mean the difference between a dream trip or a nightmare.

Click on different parts of this climber's body and check out just some of the things he could be experiencing. How would you like to be in his (cold, damp) shoes?—Gay Mohrbacher