When the lawless enclave was demolished in 1994, it was replaced with a Qing dynasty-style park that serves as a popular backdrop for taking wedding photos and filming costume dramas.

Today, Kowloon City is a bustling neighbourhood famous for its authentic Thai restaurants thanks to a burgeoning Thai community that began to take root when the old Kai Tak airport was still in operation. Many of these migrants have picked up Cantonese quickly because of the similar tones in their native tongue.

Sae-lee Suraj, 58, runs Pee Long Thai Traditional Food in Kowloon City and has lived in Hong Kong since 1991.

"We used to have a lot of flight attendants visit our restaurant. Or there would be crowds of people who dined here after sending their loved ones off at the airport. But it was very quiet for a couple of years when the airport moved away [in 1998]."

Suraj says Kowloon City is reviving, with Kai Tak as one of the stops along the Sha Tin to Central MTR rail link, which is expected to be completed in 2018.

Looking at the idyllic pavilions and lush floral greenery today, it is hard to imagine the walled city as 2.63 hectares of tightly packed dilapidated buildings without water supply or garbage-collection service and with minimal police patrol - a place 40,000 people called home.

It was also a location strategically picked by imperial Chinese officials as early as the 15th century. The Yamen - a Qing dynasty (1644-1911) military building - stands as the only remaining building from the walled city. At different times, it served as a home for the elderly, a school and an almshouse. Now, the space is being used for an exhibition about its own history.

The walled city fell through a constitutional loophole in 1899 and was governed by neither the British, Chinese or Hong Kong authorities, allowing the enclave to fester into a hotbed of vice with rampant drug use, prostitution and gambling activities.

While the physical city no longer exists, memory of the place lives on. Yip Tak-wai, 57 is the director of the Kowloon Walled City Kai Fong Welfare Continued Promotion Association, which operates a centre in Wong Tai Sin, where many former residents have moved. The association played a key role in ensuring the residents received fair compensation for their demolished homes.

Today, it still gathers the former residents a few times a year for reunions. It also offers fine arts classes for people in the neighbourhood.

Yip grew up in Kowloon City living in a cramped room which housed six people. He bought a 400 sq ft flat inside the walled city in 1976 for HK$30,000, which was only half the price for a same-sized flat outside.  

A misconception is that the walled city was home of the poorest. "[But] when they were tearing down the buildings, they found that a lot of the homes were quite nicely furnished," says Yip, who was then an accountant working in Central.

As for crime, Yip says that the triads and drug abusers did not bother locals and kept their business on the fringes of the city. People made a living inside the walled city, at factories producing clothes, plastic flowers and snacks that would be sold outside the enclave.

"You know the fishballs that Kowloon City is famous for?" Yip says. "They would be made in the walled city and sold outside."

Foreigners were sometimes more drawn to the image of the nefarious side of the city. Shintaro Nakamura, a Japanese photographer, took a series of pictures right before the walled city was demolished.

In one of the photo captions, he described the city as a "den of evil" in Japanese and depicted it as a frightening place to visit.

But not for Ng. "We would just play ping pong in the hallway," he says. "The kids would go onto the roofs and leap from building to building, or we would drag discarded mattresses to the roof and jump on them. It was a happy time."