Anmar Frangoul looks at two cities and what they've done to become sustainable. Songdo, a city being built on reclaimed land in South Korea, will cost about $40 billion. It has underground tubes to suck household waste directly to processing plants, and sensors that monitor buildings and streets to make heating and lighting more efficient. And Hamburg, Germany, boasts the world's first housing development that is powered by algae. "This translates into higher sales values, or translates into higher rents, and therefore higher property values," says developer Jonathan Thorpe. "So we think ... [there] is a fundamental economic incentive, and economic benefit, to sustainable design."