Kowloon Walled City
The fortress-like Kowloon Walled City of Hong Kong owes its origin to the fact that the land (originally a military fort) was not part of the British agreement with the Chinese at the founding of Hong Kong.
It developed into a ‘no-man’s-land’ following WWII and a tightly compacted city resulted with buildings up to 10 stories high. Streets were 1-2 metres wide with fluorescent lighting to compensate for the lack of sunlight in the lower levels (http://io9.com/#!5512888/the-walled-city-where-sunlight-couldnt-reach). It is thought that 33,000 people resided within the Walled City in 1987 with a population density of approximately 1,255,000/km2 (http://en.wikipedia.org/wiki/Kowloon_Walled_City).
The Kowloon Walled City was demolished in the early 1990s and a park was built on the site — including a scale model of the Walled City.