I hadn’t heard about the Kowloon Walled City before:
Inhabiting a block the size of the Tokyo Dome, Kowloon Walled City resembed a living, breathing creature, born from its inhabitants over its long lifespan. But the walled city was more than a physical conglomeration of buildings and people, it was an inadvertent symbol of the long struggle between China and Hong Kong, ruled by neither. It was an “in-between zone” whose remarkable existence today can best be comprehended through images, statistics and interviews.
Wikipedia has more details about it:
By the early 1980s, Kowloon Walled City had an estimated population of 35,000. Being a lawless land, the city was notorious for its excess of brothels, casinos, opium dens, cocaine parlours, food courts serving dog meat, and secret factories. The Kowloon Walled City was also infamous for its ridiculously high number of unsanitary dentist clinics, since this was where unlicensed dentists could operate without prosecution.
Over time, both the British and the Chinese governments found the massive, anarchic city to be increasingly intolerable – despite the low reported crime rate. The quality of life in the city, sanitary conditions in particular, was far behind the rest of Hong Kong.
After the Joint Declaration in 1984, the PRC agreed with British authorities to demolish the City and resettle its inhabitants. The mutual decision to tear down the walled city was made in 1987
(Thanks Matt, great find!)