55 stories above the streets of Singapore, the Sands Skypark in Singapore provides a swimming pool, casino and greenway held aloft by three skyscrapers. The skypark is almost 1,250 feet long and the pool itself is 500 feet long.
What happens if you go over the side of the pool? You and the water get safely dumped into a basin that pumps the water back up to the pool. You, presumably, will have to walk up stairs or take an elevator back up to swimming altitude.
Click on the link at designboom for more information about the Sands Skypark and its swimming pool in the sky!