2008 World Expo in Zaragoza, Spain

When the World Expo opens in Zaragoza, Spain, next year, fairgoers will encounter a building with walls made from water.

The water will come from thousands of little jets that can be switched on and off, rapid-fire, by computer-controlled sensors.

The resulting effect will enable images and text to scroll in the water walls. Or as a person approaches, the sensors could shape the water flow to make a door appear anywhere in the wall, and then close it after the person ambles through.

The 5,400-square-foot building will also be able to vanish in moments, as the roof can be lowered from its 16-foot height all the way to the ground.

The Massachusetts Institute of Technology architects who developed the idea say it's a boundary-pushing artistic statement, in the tradition of the Crystal Palace and White City of long-ago world's fairs. Current estimated cost is about $3 million.

"One of the dreams of architecture in recent years has been to create reconfigurable, interactive, dynamic buildings, but of course if you do it with bricks it's not so easy," MIT researcher Carlo Ratti said.

The theme of the Zaragoza fair is water and sustainable development, and Ratti points out that by using all recycled water, which in turn provides evaporative cooling and no need for air conditioning, the building has a low environmental footprint.

The World Expo takes place in Zaragoza June 14-Sept. 14, 2008. An estimated 6 million people are expected to attend. The Expo is the contemporary descendant of the popular World's Fairs of yesteryear, including the first in London in 1851, the famed 1893 Chicago World's Fair, and the 1964 New York City World's Fair.

Details at http://digitalwaterpavilion.com or http://expomuseum.com/2008/.