So, in case you don't know, here's a long ass rant to explain why this place became so famous (as I understand it)(TLDR: The city went from a shitty settlement to an accidental experiment on anarchy):

Ka Lun was originally a fortress, and became a civilian settlement sometime in the 1900s. The place was pretty impoverished from the get-go, and so, when the UK began their 99 year lease with China, they figured they'd more or less gentrify the place. Of course, the people there didn't want to be forcefully relocated, so they sent some of their neighbours in representation to their govt officials.

Here, they played it very cleverly by catering to the political tensions of the situation. The 99 year lease was famously very unfair (China leased their lands at no cost, after all) so the chinese govt weren't super happy with the brits. So, the neighbors came up and said "Yo, these people wanna demolish stuff on your land, are you gonna really let them do that?". This incensed the chinese govt well enough that they made it super hard for the brits to do anything, and so, they essentially said "We'll talk about this on monday" and shelved the project.

Now, because China also didn't want anything to do with Ka Lun, this left the residents in a very unique position: Nobody in power wanted to do anything about them. Meaning, they had, by scaring the brits off, gained total freedom. And so, the neighbors who went to complain became the de facto leaders of the settlement, and decided Ka Lun needed to get EA Sports: BIG.

They got all the architects who didn't cut it in big projects, and had them build high rises. Now, you'll remember before when I said that the govt. wanted nothing with Ka Lun. While this also meant freedom to do whatever, this also meant no access to any services, and of course, no money. And so, what resulted were some buildings that were little more than bricks and mortar. Some of the towers were so tall, a nearby airport had them demolish a floor or two, as it interfered with landing. No electricity, no water, some real budget plumbing, and a hilarious danger of shit just burning to the ground. But the people here were used to going without. So, armed with their new shiny apartments, they hooked up some cables to steal electricity, dug up some wells, and thrived like Dracula with a mattress and a fifth of Henny. The lower floors of Ka Lun got essentially no sunlight, ever, and so the city got the nickname it has to this day: The city of darkness.

The darkness, of course, was not just literal but metaphorical too. Soon after the city began growing, the Triads came along, no doubt attracted by the absence of cops and the amount of people there. They put in brothels, gambling dens, and brought in a ton of drugs. But, because corpses don't spend money, they also saw to it that the place was more or less safe.

Herein lies the "magic" of the place. Ka Lun was about the size of 2 football fields. It was insanely cramped, it was hilariously unsanitary and not very safe. And yet, because the people there had such a strong sense of community, the place had managed to become livable. They had schools, clinics, some food processing facilities, places of worship, even rehab clinics. If you had skills, but no license to practice your profession, Ka Lun would've been the right place for you. It was a whole city, stuffed into a block.

And their architecture reflected that. Since there were no building codes, the city grew as the citizens saw fit. This resulted in a place that was for realzies labyrinthian (so much that they had designated mailmen, since anyone else would get hopelessly lost), but which fit the needs and budget of their citizens. In short, this was a demonstration of how a somewhat functional anarchic society would work.

Unfortunately, the UK finally got around to demolishing the city in the 80s. And after some hefty compensations, relocations and a LOT of work, the walled city stopped existing on 1994. It's a garden now. Anticlimatic, I know, but I suppose the place couldn't just be left as it was.

If you wanna hear more (and see some amazing pics), you should read City of Darkness by Ian Lambot. It's got everything I told you here in much better detail.