|Map of the Mariana Trench with Challenger Deep's diving spot located. From Wikipedia|
The trench is one of the biggest geographical features on Earth. The dimension of the trench are 35,800 feet (10,910 meters) deep, 1,580 miles (2,500 kilometers) long, and 43 miles (69 kilometers) wide.
Cameron's exploration beats my by far my personal submarine diving best of a hundred or so feet off the Cayman Wall next to the Cayman Islands.