To most of us who have heard of the infamous Walled City of Kowloon but have never seen or been there before it was demolished, just looking at the pictures alone would've raise some fascination about the place. It was one of the most densely populated places in the world. A book was written depicting the lives of the people living within the concrete walls before it was demolished; appropriately named the City of Darkness as the buildings were so densely packed together residents could hardly get much sunlight. Despite there was little planning or design of the buildings from the start, the city grew throughout the decades becoming an architectural magnificence in itself.
Beyond it's rich history I could imagine there also many interesting stories to tell from former residents who was living there. At one point it's a city of lawlessness where British rule had little effect on the place, it was an infestation for triads, drug dealing, prostitution and other criminal activities. On the brighter side, it was also a thriving community for families and businesses.
It would've certainly be a perfect environment setting for comic books and films, and in fact it has been featured in various popular media such as Bloodsport (with Jean-Claude Van Damme) and the Japanese manga Blood+. Here's a few interesting links:
Lots of pictures and info:
Also check out this cool cross section illustration of the Walled City, which was from a Japanese book. The details are amazing, but I'm not sure if there are any higher resolution of the pictures out on the internet and no luck on Google image search from me either.