In this video segment adapted from Interactive NOVA, mountain-climber Rob Taylor gives a harrowing account of his failed attempt to scale the peak of Africa's Mount Kilimanjaro. Because it is a free-standing mountain—the tallest in the world—climbers must ascend from the base through several climate zones before reaching the arctic summit. After being rescued from a fall near the summit, Taylor thought his worst problems were behind him when an unanticipated consequence of his descent to warmer temperatures presented an equally dangerous challenge.