Waterfall Swing

(Video Link)

Whee! Swing through a waterfall and never get wet on this installation by Mike O'Toole, Andrew Ratcliff, Ian Charnas and Andrew Witte. The water pours down only when the riders aren't passing through the nadir of the swing's arc. Here's how it works:

Water recirculates through 273 independently controlled solenoid valves at the top of the structure to create a wall of water. This water starts from a collection pool on the ground and is pumped up to a large pipe that feeds the solenoids. Sensors mounted on the swingset gather information about the angle and speed of each swing. That information is sent to a computer that predicts the action of the rider. The computer then creates a hole in the wall of water, allowing the rider to swing through without getting wet.

Link -via Colossal