Xingtai, China

This city of 7,111,106 residents is not for the faint of heart. The air quality is notoriously bad, ranking Xingtai as the most polluted city in China according to a 2013 survey. And with a history of major earthquakes - including a 7.2-magnitude quake in 1966 that killed over 8,000 people - the bureaucratic headaches and safety concerns are persistent. On the upside, Xingtai is an important industrial hub, producing 20 million metric tons of coal annually and hosting a massive 2.06-gigawatt power plant. But for most, the heavy environmental toll and disaster risks likely outweigh any economic benefits.