Found a fantastic blog post on Coilhouse (go read for more details and nifty video), on Kowloon Walled City-- a dystopian monolith of overgrown urbanization which existed in anarchic limbo in the middle of Hong Kong between 1945 and 1993.
Kowloon's bizarre state of lawlessness attracted thousands of people-- drug dealers, unlicensed dentists, entrepreneurs, refugees-- and the city's population boomed to a high of 50,000, making it one of the most densely populated areas on the planet. Thousands of makeshift expansions were built to cope with the growing population, and the city developed into 14-story monolith, a place where sunlight rarely reached street level and denizens drilled down to tap into water pipes from surrounding regions of Hong Kong. The city was evacuated in the early 90's and demolished in 1993, but its legacy now lives on in popular culture-- it is the basis of dozens of dystopian cities created in movies, books, and video games. Quality of life and sanitation were poor, but the reported crime rate was low, and many small shop owners found it a city of unique opportunity.