Hidden in the shadows of a bustling city lies a land of filth and utter despair. This is Along Pi, a wasteland just 30 kilometres away from the Cambodian tourist hub of Siem Reap, which is famous for the incredible temples of Angkor Wat.

Every day tonnes of waste are dumped here, forming mountains of toxic compounds and an accompanying stench that is as overpoweringly putrid as it is unimaginable.

Hundreds of poverty-stricken locals are forced to wade through the filth in a bid to find previous recyclable materials such as glass, paper and metal, which they can sell. If they’re lucky, they will make $2 per day.

Tragically, many of the workers are children.

Spanish-born David Rengel visited the dump site to document child labour issues in late 2014, and ended up helping to expose one of the darkest sides of tourism we’ve ever seen.

It’s a wake up call to the world that we must hear before it’s too late.

Mr Rengel said the wasteland has morphed into a voyeuristic tourist stop with guides — a place where dozens snap photos of the unfortunate workers.

“When I got to the landfill my initial work was focused on child labour but while I was doing my report I saw that tourists began arriving, sometimes in buses and other times in tuc-tucs (Cambodian taxis),” Mr Rengel told news.com.au.

“It was awful … I asked the people who live and work in the dump if it was an isolated case or if it was frequent and they told me that every day tourists arrive to the landfill.”

He said the first to arrive was a bus carrying 20 tourists, who wore masks to prevent breathing in toxic gas from the garbage.

“They were perfectly aligned and followed their tour guide. They were taking photos of families who work in the landfill but mostly they were looking for children, they wanted to take pictures with them. They gave some candy to the children.”

Rengel said one tour guide he approached claimed the group were medical students, but he was concerned why they didn’t have any medical instruments with them.

His shock is echoed by the charity Friends-International, which assists marginalised urban children around the world.

It has been working with families at Anlong Pi since 2010, which is describes as “a stinking, dirty and dangerous dumpsite, where the daily detritus of Siem Reap provides a working and living environment for hundreds of people — women, men … and children”.

It has also issued a call for an end to the practice on its website.

“Recently, the staff have noticed many more tourists coming to take photos of the site and hand out food support and money to those who work there. They often come in mini-vans/buses, and as organised tour groups,” they write.

“This poses a great risk to our work as families are tempted to bring their children (who would normally be at our preschool/non-formal education or actually in public school) onto the dumpsite to beg.

“The behaviour of these dumpsite tourists may be well-meaning, but not only does it jeopardise our work it actually harms the children we are trying to help find alternatives for.”

Ultimately, there are just some places that shouldn’t be on the guidebook.