Here are some websites about the place. Its really was something out of a science fiction movie, now its a park.

Here is some historical info with pictures.

http://www.doobybrain.com/2008/05/01/my-father-lived-in-kowloon-walled-city/
http://zeekeekee.wordpress.com/2009/05/05/kowloon-walled-city-something-out-of-a-science-fiction-story/

This is a website by the government http://www.lcsd.gov.hk/parks/kwcp/en/index.php