ON THE EVE of New Year's Eve, expedition prep is in full swing at the Homestead. Isaacs has flown in, and most of the team (minus Theo, who's getting remarried in two weeks) is getting down to brass tacks as the launch date approaches.

Since the Hollywood schmoozefest, climate change has remained big news—thanks in part to the release of the UN's latest report on the subject, a six-year effort that offers a gloomy assessment of planetary health. Laurie David and Steger have started cross-pollinating with shared Web links; Isaacs is negotiating to use an unreleased Tupac song in the teaser's soundtrack; and Lloyd Phillips, the Sony producer, has passed word about Baffin Island to a friend who passed it on to billionaire Richard Branson. Branson got excited, and he and his 21-year-old son, Sam, are joining the trip for the last two-week leg.

"We haven't even tried to go after celebs yet," says Isaacs. But the list keeps growing anyway: Mountaineer Ed Viesturs has committed to a two-week stint; Cheryl Tiegs will fly up for a week with Howard Ruby; even Pierce Brosnan might make an appearance.

"We're definitely on good footing in L.A.," Steger tells me later. "But I was really there to make long-term relationships."

In 2008, Steger will kayak the open water of the Weddell Sea. In 2009 he and the team will head to Greenland for another overland dogsled trek. "Western Antarctica and Greenland will determine the fate of our civilization," Steger says. "Greenland holds 12 percent of the world's freshwater, and if its ice cap becomes unstable, it could be catastrophic to our society."

Steger and Isaacs hope to parlay the next two expeditions into movie deals, too. But Steger says the movies don't mean much to him by themselves—they're strictly a medium for getting the word out faster. He's the first to admit he's in a hurry. He can't muscle an 800-pound dogsled forever.

Which may be why he's working so hard on one of his final acts: completing the construction of an ambitious, soaring structure he calls the Castle.

Taking the money he earned by licensing his name to Target—which in the late eighties created a Will Steger line of tents, packs, and sleeping bags—Steger and a few locals have been slowly erecting a massive stone, glass, and recycled-timber building. The six-story Castle, which sits on a hill and dwarfs the cluster of cabins at its base, has decks shooting off in every direction and roof angles that make it look like it's sailing across the landscape.

When it's finally finished, around 2010, the Castle will serve as the think tank for the Will Steger Foundation, drawing small groups of activists, politicians, and industry leaders from around the world to cook up new ideas about education, the environment, or whatever profound matter needs addressing.

"Thirty years ago, I realized that, to make an impact, you have to bring together decision makers," Steger tells me as we watch the sun sparkle off Picketts Lake from a Castle deck. "The setting will provide inspiration and vision. Seventy years from now, this will all be covered by virgin forest," he says, pointing to the motley buildings below.

But the Castle will endure, Steger points out. Visionary pragmatist that he is, he hopes the Will Steger Foundation will endure as well. "I'm sort of like a dreamer and a doer," he says. "A real dream is something you have to do."