Megalopolis

This is like something out of Judge Dread. Kowloon was a fort in Hong Kong leased to the English way back when. They didn't use it as a fort and people began settling there and building houses. Houses were built on houses and it slowly rose throughout the 20th century into this massive city complex complete with its own food markets (to include butcher shops), doctors, dentists and everything else one finds in a city. Some people lived there and never came out.

It was destroyed in 1993/94 as being too unsanitary and hazardous.

But what a city!