This is a pretty cool feat by James Cameron, who just returned from the bottom of the Marianas Trench - the deepest place in the world. To put it in perspective for you, if you took Mount Everest, and turned it upside down, it still wouldn't be able to touch the bottom, not by about a kilometer. James Cameron had the following to say about his experience:
It was very lunar, a very desolate place, very isolated. My feeling was ...