From the wikipedia article:
Kowloon Walled City was a densely populated, largely ungoverned settlement in Kowloon, Hong Kong. Originally a Chinesemilitary fort, the Walled City became an enclave after the New Territories were leased to Britain in 1898.
The City’s dozens of alleyways were often only 1–2 m (3.3–6.6 ft) wide, and had poor lighting and drainage.[18] An informal network of staircasesand passageways also formed on upper levels, which was so extensive that one could travel north to south through the entire City without ever touching solid ground.[4] Construction in the City went unregulated, and most of the roughly 350 buildings were built with poor foundations and few or no utilities.[19] Because apartments were so small—about 60% were 23 m2 (250 sq ft)—space was maximized with wider upper floors, caged balconies, and rooftop additions.[7][20][21] Roofs in the City were full of television antennas, clotheslines, water tanks, and garbage, and could be crossed using a series of ladders.[22][23]
Beginning in the 1950s, Triad groups such as the 14K and Sun Yee On gained a stranglehold on the Walled City’s countless brothels, gambling parlors, and opium dens. The Walled City had become such a haven for criminals that police would only venture into it in large groups. It was not until 1973–74, when a series of more than 3,500 police raids resulted in over 2,500 arrests and over 4,000 pounds of seized drugs, that the Triads’ power began to wane. With public support, particularly from younger residents, the continued raids gradually eroded drug use and violent crime. In 1983, the police commander of the Kowloon City District declared the Walled City’s crime rate to be under control.[1]
The City also underwent massive construction during the 1960s and 1970s.[4] Eight municipal pipes provided water to the entire structure (although more could have come from wells).[5] A few of the streets were illuminated by fluorescent lights, as sunlight rarely reached the lower levels.[1] Although the rampant crime of earlier decades diminished in later years, the Walled City was still known for its high number of unlicensed doctors and dentists, who could operate there without threat of prosecution.[6]
Although the Walled City was for many years a hotbed of criminal activity, most residents were not involved in any crime and lived peacefully within its walls. Numerous small factories and businesses thrived inside the Walled City, and some residents formed groups to organize and improve daily life there. An attempt by the government in 1963 to demolish some shacks in a corner of the City gave rise to an “anti-demolition committee” that served as the basis for a Kaifong association. Charities, religious societies, and other welfare groups were gradually introduced to the City. While medical clinics and schools went unregulated, the Hong Kong government did provide some services, such as water supply and mail delivery.[1]