In 1987 Kowloon Walled City packed 33,000 people into six and a half acres

By 1987, Kowloon Walled City held an estimated 33,000 residents on 2.6 hectares — "approximately 1.2 million inhabitants per square kilometer (3 million per square mile)," according to Wikipedia, making it one of the most densely populated places on Earth. The 1898 convention that leased the New Territories to Britain excluded the old Chinese fort, leaving an enclave claimed by two governments and governed by neither.

Unregulated construction from the 1960s onward created "a labyrinth of interconnected high-rise buildings built without architectural or engineering oversight." Alleyways ran one to two meters wide, lower floors saw "a near-total lack of sunlight," and the informal network of staircases and passageways on upper levels grew so extensive that "one could travel north to south through the entire city without ever touching solid ground."

Triads controlled the brothels, gambling parlors, and opium dens from the 1950s until 1973 and 1974, when "more than 3,500 police raids resulted in over 2,500 arrests and over 1,800 kilograms (4,000 lb) of drugs seized." Residents lived alongside unlicensed dentists, factories, and schools. Britain and China agreed to demolish the city in 1984, paid HK$2.7 billion in compensation, and tore it down between 1993 and 1994. A park now stands on the site.

Previously:

• Kowloon Walled City in Minecraft
• Kowloon Walled City was the densest — and most interesting? — place on Earth
• Japanese arcade recreates gritty walled city of Kowloon