The Kowloon Walled City was once one of the most densely populated precincts in the world. And by some measures, it was. Prior to its demolition in 1993, the Walled City was believed to house some 50,000 people — mostly informally — and was known for problems of prostitution, gambling, and drug usage.

But despite these problems, the Walled City is the kind of urban settlement that fascinates architects, planners, and other city builders. This is partially because it wasn’t centrally planned. There is no individual architect or specific team responsible for its design.

It was, instead, a kind of self-organizing system — both from a built form standpoint and from, I’m sure, a socioeconomic standpoint. And so it is fascinating to see what results when you let that happen on its own.

Here are a series of cross-sections of the Walled City that were meticulously drawn prior to its demolition. They obviously aren’t new, but it is the first time I am seeing them. It is interesting to see everything from mahjong parlors to strip clubs stacked on top of one another in such a confined space.

This was the Kowloon Walled City.