Isamu Noguchi's sculptures for Expo 70 in Osaka, Japan.
Another view, in daylight
We can see the red support inside the falling water, so the sculpture is not technically an optical illusion, but I find Noguchi's fountains much more magical and less tricky than, although they are related to, the fountains in this Deceptology post: 10 magical floating fountain illusions>>
Watch a short segment of a film that shows his Expo 70 fountains: Isamu Noguchi: The Sculpture of Spaces, Films on Demand>>
The Noguchi Museum>>