It’s been 20 years since Kowloon Walled City was demolished, but amazingly, it remains one of the most dense structures ever built. As many as 33,000 people crammed into the seven-acre plot, known in Cantonese as “the city of darkness,” before they were relocated in 1993. The Walled City was one of those urban anomalies that tend to pop up in disputed territories and borderlands. It began as a Chinese military outpost in the 1800s, and emerged as a kind of no-man’s-land when England leased Hong Kong in 1898. The Japanese razed the site during World War II, and after the surrender, it became a magnet for refugees when neither England or China wanted to deal with the burgeoning, ungoverned community. Kowloon Walled City, as we talk about it today, was born.In the years that followed, 300 towers rose on the site—soon, these buildings were woven into a dense interconnected network of ad hoc infrastructure. There was never an architect or planner involved, just an army of residents and carpenters who worked to fill the cracks. Without city services, residents got water from wells, and trash was hauled up to the roof. Every resident had an average of 40 square feet of living space. The Walled City was often described as a cesspool (“den of iniquity” was another favorite), but at the same time, the community was a model for cooperation: residents created basic rules to deal with matters of survival, like fighting fires. Schools, shops, and businesses (including those of doctors and dentists who couldn’t get licensed in Hong Kong) flourished. Crime was also a major problem, as you might expect—for a time in the 1960s and 70s, the Triads controlled the city. But as the SCMP describes, most former tenants remember it fondly. “We all had very good relationships in very bad conditions,” one ex-resident says. “People who lived there were always loyal to each other. In the Walled City, the sunshine always followed the rain.”In the mid-1980s, concerns over living conditions spurred officials to relocate the majority of residents, and only a few years later, the Walled City was empty.Today, the site is a park—a bronze model of the city is all that remains of its former residents.