Walking through walls will be possible and even encouraged.
When next year's world expo opens in Zaragoza, Spain, fairgoers will encounter a building with walls made of thin sprays of water. Inside, there will be normal building stuff: a cafe, an exhibition space and overhead lighting.
The water will come from thousands of little jets that can be switched on and off, rapid-fire, by computer-controlled sensors. As a person approaches, the sensors could shape the water flow to make a door appear anywhere in the wall and then close it.
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.
The theme of the Zaragoza fair is water and sustainable development.