For his sequel to Avatar , James Cameron is building a submarine that will carry him and a crew to the bottom of the Mariana Trench, 35,800 feet below the surface of the Pacific ocean, the deepest spot on earth, Britain's Guardian newspaper reported today. It said that the vessel is currently under construction in Australia, where tests on the hull have already been completed. A trial dive is expected to be completed by the end of the year. Only two men, Don Walsh and Jacques Piccard, have ever completed such a dive (in 1960). Andrew Bowen, director of the National Deep Submergence Facility at Woods Hole, told The Guardian that while Cameron's aim is not so much about scientific exploration as about making a compelling movie, both purposes are likely to be achieved. "Exploring such an inhospitable and extreme realm of the deep ocean is hugely valuable, because it creates a chance for people to engage their imagination. There is nothing quite like being there," he said.