Walking on Water.

Michael Cross' artwork, displayed in the 2006 London Design Festival, lets you walk on water:

Bridge, by Michael Cross, is a series of steps that rise out of the water as you walk across them, as if walking on water. On entering the exhibition the visitor is met by an empty expanse of water with one step at its edge: stepping on to it forces it...

http://www.londondesignfestival.com/Gallery.aspx?id=1787

UPdate 10/19/06: An better explanation of the exhibit at Pixelsumo - Thanks Jim Perry!