James Cameron–yes, that James Cameron, the one who gave us dreadlocked 3-D space eco-mystics in Avatar–is about to go where only two men have ever gone before. After developing a revolutionary submersible (a version of a submarine) behind a veil of secrecy for eight years in Australia (could this sound more cinematic?), Cameron announced this month that he plans to plunge nearly seven miles down into the Pacific Ocean's Challenger Deep, the deepest known point in the ocean. “It’s a great idea, a tremendous idea,” said Alfred S. McLaren, a former U.S. Navy submariner, about Cameron’s 24-foot, bullet-shaped submersible. In tests for his ambitious dive, Cameron has plumbed the ocean’s depth to more than five miles, setting a modern record. His ultimate challenge, however, will take him more than 6.8 miles below sea level, a dive that will require Cameron to occupy the submersible for about nine hours. Two U.S. Navy men are the only people who have made the journey before.