Inside the Kowloon Walled City (2012)

I lived 10 minutes walk from there, in 1996 or so. It's now a park that's around 5 minute walk wide. I could never have imagined 50,000 people fitting in that park!

"A thorough government survey in 1987 gave a clearer picture: an estimated 33,000 people resided within the Walled City.[8] Based on this survey, the Walled City had a population density of approximately 1,255,000 inhabitants per square kilometre (3,250,000 /sq mi) in 1987. For comparison, Hong Kong as a whole (itself one of the most densely populated areas on Earth) had a population density of about 6,700 inhabitants per square kilometre (17,000 /sq mi) as of July 2009.[26]" http://en.wikipedia.org/wiki/Kowloon_Walled_City