Conjure up the most energy-efficient building you can: the roof would collect rainwater for recycling. Lights and appliances not in use would turn off by themselves. And the structure itself would be built using predominantly recycled materials. In April, the Hearst Corporation's Manhattan employees will begin to move into such a place: their new headquarters will be New York City's most environmentally friendly skyscraper. The architect is Norman Foster, famed for the Millau viaduct in southern France and London's Swiss Re building. Hearst Tower, his debut large U.S. project, is the first office building in New York City to garner a gold rating from the U.S. Green Building Council's Leadership in Energy and Environmental Design scheme, the recognized U.S. standard for building sustainability. "My mission is to create a structure that is sensitive to the culture and climate of its place," says Foster. The structure will practice what the architect preaches: enter the building and you'll be greeted by Ice Falls, a three-story waterfall that uses, yes, collected rainwater to cool and humidify a six-story atrium. And sensors will monitor energy usage and readjust it during off-hours. Foster's latest environmental commitment soars 42 floors up—a shimmering stack of steel diamonds. The tower itself rises out of the original Hearst building, a 1928 Art Deco landmark. "The project ultimately succeeded because we had the good fortune of working with a progressive owner that was determined to advance these principles in New York City," says Foster. "Environmental sustainability is a product of that holistic way of thinking." He's spreading his ethos: Foster's Tower Two at the new World Trade Center will also be green.