Take a look at this:

Welcome to the Kowloon Walled City. Looks like a scene from Bladerunner’s underworld or some crazy photomontage by Filip Dujardin, but built, and demolished 10 years ago.. The density of this place was about 1,255,000/km2 – making it the densest recorded place on the planet – housing some 33,000 people on a lot measuring 210 by 120 m, a bit more that two soccer fields.


Image courtesy and an interesting blogpost on the Kowloon Walled City: http://worldphotocollections.blogspot.com/2010/06/kowloon-walled-city-hong-kong-china.html

More images here;

…and a Wikipedia article here.