Got an old airship hangar lying around and not sure what to do with it? If it strikes you as odd to have a water park in a desert, Germany has built an entire tropical resort indoors, big enough to hold the Eiffel Tower lengthwise, and where the temperature is a constant 78.8F. It’s the largest free-standing hall in the world, with the largest indoor beach. It also has a water park, featuring a high-speed turbo slide that whips you along at over 40mph.