Hongqiao, China

This industrial hub is no picturesque paradise. Hongqiao's population of 58,287 lives amid the gritty realities of one of the world's largest aluminum producers. The company's rapid expansion has repeatedly brought it into conflict with environmental regulators, who have cited the firm for unauthorized construction and emission breaches. And while the group is working to cut its carbon footprint, the energy-intensive nature of aluminum smelting means bureaucratic headaches and sustainability challenges will likely persist. Overall, this is a city for the hardy, not the faint of heart.