Forces of Nature

In 1999, the California Academy of Sciences, eager to replace its quake-damaged building, invited six architects to submit designs for a new home in San Francisco's Golden Gate Park. The facility had to accommodate 38,000 live animals, 20 million specimens, and 2 million visitors a year -- and meet lofty environmental goals.

Five architects arrived with intricate models. Renzo Piano had only a pad and a felt-tip pen. After days of talks and walks in the park, he climbed onto the Academy roof, gazed at San Francisco's hills, and came back down with a winning design: a wavy green line. "The idea was to make the roof like a flying carpet, a piece of the park flying," he says. "If you fly over the park now, you don't even see the building."

The disappearing act took 320 engineers from the design firm Arup to orchestrate. "When we drew all those curves, I knew that was going to be a great challenge," says Piano. (So great, in fact, that the Discovery Channel's Extreme Engineering did an episode on the project.) The biggest conundrum: how to support the glass over the central piazza, because Piano refused to let columns break up the space. The answer came, of course, from nature -- a spiderweb of cables now holds up the glass.

Piano's $488 million vision opens to visitors on September 27.