Though thousands of adventurers have scaled Mount Everest, the highest and most famous of the world's 14 tallest mountains, only 40 climbers have conquered them all. Located in Asia's Himalayan and Karakoram ranges, the "eight-thousanders" each stand over 8,000 meters (26,247 feet) tall, above the so-called "death zone," where the amount of oxygen is insufficient to sustain human life for an extended period.