Castles built on sand never stand the test of time, but cities which float on water could change the world. A nonprofit group called the Seasteading Institute believes floating cities will free humanity from politicians and enrich the poor. They also believe they will be good for the environment. It sounds like something out of a science fiction film, but this isn’t just a crazy pipe dream. PayPal founder Peter Thiel is bankrolling Seasteading’s radical plans to introduce the first floating city by 2020.