Above is the world's largest freestanding building, an airship hangar built a decade ago at an abandoned Soviet military base south of Berlin. The $110 million hangar — 1,181 feet long by 688 feet wide by 351 feet high — held a massive airship that entrepreneur Carl von Gablenz hoped would prove that such vehicles were ideal to deliver massive industrial machinery like oil rigs and wind turbines. But in 2002, von Gablenz's company, Cargo Lifter AG, was out of cash. A Malaysian firm, Tanjong, bought the hanger for $24 million and converted it into Tropical Islands Resort, a huge water park. From Air & Space:

Tanjong soon found that keeping the hangar at 78 degrees Fahrenheit year-round was a challenge. So workers welded shut the two steel doors, which weigh 600 tons each. To open the hangar to light, "we exchanged the [steel] skin of the hall with 20,000 square yards of translucent film," says Tanjong spokesman Patrick Kastner. "This makes natural tanning possible…"

At 3,000 square yards, (the pool is) larger than four Olympic-size pools, and its artificial horizon conjures a faraway island. At the "shoreline" are 600 feet of sandy beach and hundreds of deck chairs. The Bali Lagoon has a grotto and waterfall, as well as the world's largest indoor rainforest, with 50,000 trees in 600 varieties–from palm to papaya–that thrive in natural light. Its most popular attraction is a nine-story waterslide that propels sliders to 44 mph.

