Do you remember in "It's a Wonderful Life" when Jimmy Stewart and Donna Reed fell into a pool hidden underneath a retractable gym floor? Here's the scene to refresh your memory.
The place actually exists. It's called, fittingly, the Swim Gym, and belongs to Beverly Hills High School in Los Angeles. Here's how it works: The court is divided along the centerline, and each half is anchored to rows of two-by-fours atop steel I-beams. The court "opens" at the turn of a key — motors roll the platforms underneath the arena bleachers, where huge exhaust fans mitigate moisture. Then, 5 feet below, a 25-yard swimming pool appears.
The installation went much more smoothly than the dance scene in the movie. Nothing — man, woman or machine — fell in.