Kowloon Walled City was a densely populated, largely ungoverned settlement in Kowloon, Hong Kong. Originally a Chinese military fort, the Walled City became an enclave after the New Territories were leased to Britain in 1898. Its population increased dramatically following the Japanese occupation of Hong Kong during World War II. In 1987, the Walled City contained 33,000 residents within its 6.5-acre (0.03 km2; 0.01 sq mi) borders. From the 1950s to the 1970s, it was controlled by Triads and had high rates of prostitution, gambling, and drug use.
And here, in four parts, is a German documentary made about the city itself. Because the Walled City no longer exists, this documentary is something of an artifact. Excellent viewing.