In Bangkok, the capital city of Thailand, there are countless things to see and do. However, one hidden gem that goes unnoticed by most lies in an unexpected place – in the basement of an abandoned shopping mall.

Tucked away behind a gate, where you would almost never notice it, is what used to be the New World shopping mall. The former retail center was built in the 1980s but closed in 1997 after it was found to have breached building regulations; the mall was 11 stories high, 7 floor taller than the approved construction blueprint.

A couple years later, in 1999, the building burned down. While the exact reason is unconfirmed, some believed it was set aflame because it was too tall. Many people in old town Bangkok find it insulting to build something taller than the Grand Palace, so the size of the mall may have angered people.

In the fire, the mall lost its roof, causing rainwater to accumulate in the basement and flooding it year round. The stagnant water resulted in a major mosquito problem and, in an effort to get rid of the pests, locals started introducing tilapia to eat the insects.

It didn’t take long for the fish population to thrive, today over hundreds of them swimming around rusty escalators and across the 5,000 square foot floor. The abandoned building has turned into an amazing self-sustained, urban aquarium.

Backpacker Jesse Rockwall stumbled upon the mall when traveling through Thailand and shot several photos of the urban wonder. He certainly found the basement abnormal, stating, “It is quite bizarre – I was really surprised when I came across it. It is literally three blocks away from backpacker central, but nobody is even aware it is there.”

He also explained, “It was very quiet in the mall, I could only hear the sound of splashing fish, even though it’s close to a main road”

Visitors can also feed the fish by purchasing fish food from various shops around the mall. However, throwing anything else into the water is banned in order to protect the fish.