Kowloon Walled City, China

Like something out of a post-apocalyptic Phillip K. Dick story, Kowloon was a densely populated, nearly lawless city. In its final year of existence, it housed 603 Chinese per 5,000 square feet (compared with 16 people per 5,000 square feet in lower Manhattan). The city began as a military outpost but after the failed Japanese occupation of Hong Kong during World War II it became a crowded refugee city with 2,000 residents by 1948. With no government enforcement or local law to tell people what to do, the city quickly became a center for crime.