4. Beijing National Aquatic Center

Location: Beijing, China
Website: waterpark.water-cube.com

This building was constructed for the 2008 Summer Olympics. Once those were over, they converted half of the massive building into a water park. It's a very cool looking building, both outside and inside, and some kudos go to China for repurposing what could have been a monumental, single-use waste of space into something that makes more sense.