Kowloon Walled City was a dense, overpopulated, and largely ungoverned 6.5 acre enclave in Hong Kong (demolished in the 90s) that at one point housed 50,000 residents. It grew to swallow up roads until it became a dank maze of corridors and warrens with little light, ventilation, electricity, or water. Like something out of JG Ballard's writings, some people spent their whole lives in this lawless settlement that seemed like another world.
These people were the fortunate ones, who had an exterior wall.
Brief respites on the roof to fight the claustrophobia of windowless flats and corridors.
Grocery store:
http://en.wikipedia.org/wiki/Kowloon_Walled_City
This documentary is one of the only films ever made inside.
Amazing cross-section drawing done by researchers:
