I came across a video on Youtube discussing it (there are several), and Kowloon Walled City is just endlessly fascinating. A few notable videos I found on the subject were:
There is also a book on the city called City Of Darkness Life In Kowloon Walled City, which I found on archive.org in high resolution. It is full of photographs and detailed accounts of the comings and goings within the enclave.
Curiously, in cyberpunk media this sort of mega-slum is often portrayed as an excess of capitalist urbanization, whereas in historical reality it was an exclave of "communist" China inserted into "capitalist" British Hong Kong, wherein the "capitalist" authorities had no jurisdiction.
(Edited: Sounds more like the point was that it was effectively nobody's jurisdiction.)