Marianas Trench in the South Pacific
The deepest point of the world's oceans, the Mariana Trench, could swallow Mount Everest whole with more than a mile to spare. In 1960, U.S. Navy Lieutenant Don Walsh and Jacques Picard in the bathyscaph "Trieste" reached the bottom of the Trench at 35,840 feet deep. The vessel spent barely 20 minutes on the ocean floor, and only unmanned vessels have been back since. While man's desire to explore the earth's bottom is just as great as reaching its top, the ocean floor is no mere curiosity. Previously unknown organisms that can survive extreme pressures and utter darkness could be uncovered, and the Trench could yield new insights into plate tectonics and earthquakes. It's no exaggeration: four-fifths of the Earth remains largely unexplored and the Mariana Trench is the planet's deepest mystery.