In January 1987, the Hong Kong government announced plans to demolish the Walled City. After an arduous eviction process, demolition began in March 1993 and was completed in April 1994. Kowloon Walled City Park opened in December 1995 and occupies the area of the former Walled City. Some historical artifacts from the Walled City, including its yamen building and remnants of its South Gate, have been preserved there.
It's only 4 square meters per person to live.
At one time, one of the most densely populated areas on Earth, Kowloon, was a walled city within Hong Kong. It was unregulated by the then-ruling British authorities, who reluctantly allowed it as the only Chinese settlement. It was a no man’s land because of this; run by the Chinese mafia and filled with brothels, sweat shops, illegal hospitals, and trashy eateries.
98% of the area in Kowloon Walled City have no sunshine all the time.
Originally, Kowloon was built as a watchpost for guards who would protect the area from pirates. But as the population grew–from 10,000 in 1971 to a staggering 50,000 in 1990–attempts were made by the government to evict the squatters living in the city. In 1992, the governent succeded in evicting the population and, in 1993, the 15 story tall block of buildings was torn down. Today, a park with tennis courts covers the area.
Below you will find a highly detailed cross section of the city, drawn by a Japanese team, just before it was torn down. They were obviously having fun drawing and added many hidden gems of city life. 
The Kowloon walled city today has been transformed into a park,this is the model of the Kowloon walled city which palced in that park.
Refer:http://www.imdouz.com/Hongkong-Jiulongzhaicheng/
http://en.wikipedia.org/wiki/Kowloon_Walled_City
http://www.visualnews.com/2011/01/05/kowloon-walled-city-pictures-and-cross-section/
