According to National Geographic, James Cameron's trip in the Deepsea Challenger submarine took him 35,756 feet (10,898 meters) deep. He traveled where only two men have ever gone, to the Challenger Deep valley of the Mariana Trench (the deepest part of the ocean).
"Falling through darkness--that's something that a robot can't describe," Cameron said. "Most importantly, though, is the significance of pushing the boundaries of where humans can go, what they can see and how they can interpret it." Source: Yahoo
This was the first journey to the bottom of the Mariana Trench in 50 years. In 1960, two explorers, Jacques Piccard and Lt. Don Walsh, descended in their submarine, the Bathyscaphe Trieste, to break the all-time human depth record - 35,813 feet (12,138 meters). During the dive, the Rolex Deep Sea special was strapped to the outside of the sub. Needless to say, the Rolex and the explorers both survived the journey intact.
Fifty years later, James Cameron descended to the bottom of the Marina Trench, with the Rolex Deepsea Challenge strapped to the outside of the sub. The new watch was specifically created for this dive, and is rated to 12,000 meters (39,370) - it made it down and back with no problem.
Editor's Note: James Cameron wore a Rolex inside the sub, but the Rolex Deepsea Challenge watch was strapped to the outside of the submarine.