The first time Brett Patman entered an abandoned building, he panicked.

It was an old denim factory in Melbourne, and Patman — who had worked in similar spaces as a service technician — was worried he was not alone.

The first room he entered had been devastated by a fire. He took a few snaps with his phone and sent them to his wife. She sent back exclamation points.

"The more I sort of progressed through the building, the more evidence you see of people having been there," he says.

He went into a warehouse area and found a bike leaning against a pole.

"I started thinking 'Oh, God, there is somebody else here'."

He'd come to take photographs — he'd listened to a podcast about abandoned photography and had been playing around with a camera — so he took some shots and left.

"It all pretty much came from there," he says.

"It sort of became a bit of an obsession."

Behind the bar at the Terminus Hotel, abandoned for three decades in central Sydney. ( Supplied: Brett Patman )

Patman, 36, is now a full-time photographer, publishing his work under the banner Lost Collective.

He is one of the foremost proponents, in Australia, of urbex, or urban exploration, a kind of guerilla photography that aims to illuminate the spaces humans leave behind.

For Patman, there is a wonder and a mystery to these places. For his social media followers — and he's got quite a few — there is sometimes a personal element.

"Once I started the project, and publishing these galleries through Lost Collective, people started actually connecting with them, and then there was this real-life history that was coming out through the posts," he says.

"People who actually were at these places started to come out and say, 'I used to work here, Dad used to work here, show Dad, show Uncle Bob'."

Chairs left in an empty ballroom at the Fallside Hotel and Conference Centre in Niagara Falls. ( Supplied: Matthew Christopher )

Early on, he explored what remained of Sydney's Callan Park Hospital for the Insane, opened in the late 19th Century, and posted the results to his Facebook page.

Sydney photographer Brett Patman. ( Supplied: Brett Patman )

The response, he says, was mixed. He heard stories from people who said their family members had been bashed by fellow inmates or subjected to electroconvulsive therapy, at that stage a fairly new form of psychiatric treatment.

"But then a lot of the people who worked there, and the nurses who helped people, they took issue with some of the connotations that were coming through with that, and I realised there is two sides to the story here," he said.

The comments section of Patman's Facebook post became a kind of forum of shared memory.

"When you get to that much of a personal level with the history of it, it's hard not to really want to dig deeper and find out whatever you can, good and bad," Patman says.

"And that's a big part of what drives what I do today."

'Ominous, creepy, serene, beautiful'

Matthew Christopher, 39, had been working in mental health in Pennsylvania for years when he heard about an old hospital near his home. He went to go see it.

That was the spark.

Pretty soon, Christopher was exploring other abandoned hospitals. Then schools, factories, power plants. He started taking along a DSLR.

"I wanted to be able to share with people what I thought made the places interesting or significant or beautiful," he said.

Christopher now travels full-time across the United States photographing abandoned spaces.

The interior of the Randall Park Mall, a shopping centre in the suburbs of Cleveland opened in the 1970s and closed in 2009. ( Supplied: Matthew Christopher )

His work, under the title Abandoned America, encompasses a blog and two books, the second of which was released late last year. He has tens of thousands of Facebook and Instagram followers.

"Some places are very ominous and very creepy," Christopher says.

"Some places are very tranquil and serene and beautiful."

Other places are just sad, he says, particularly when they illustrate how much a city or town is struggling.

"It's sort of a bit like a parallel universe, right? What does a school become when it's not teaching people?" he said.

Something he has noticed through his work recently — something that feels extra significant in light of Donald Trump's electoral victory — is a sense of shame some communities feel at becoming victims of economic dislocation.

"They feel like it's their town, and it's just the areas that they live, and other areas must be doing better," Christopher says.

"Overall, we are taught that economic prosperity is equal to morality, to being a hard worker and pulling yourself up by your boot straps — and if you're struggling to do that, there must be something wrong with you."

A wall inside Pennhurst State Hospital, an abandoned facility in Pennsylvania. ( Supplied: Matthew Christopher )

One of the thornier aspects of this work: the legal one

"I do quite a bit to get permission" to enter spaces, Christopher says.

"But I'd also be a liar if I said that I only ever get permission and that I haven't trespassed."

He's had some "relatively tense" interactions with security, he says. He tries to remain respectful and to cooperate.

A hallway inside the Terminus Hotel. ( Supplied: Brett Patman )

"One of the hand, I can understand somebody saying, 'Hey, this is private property, keep out'," he says.

"But on the other hand, using the example of the asylum [in Pennsylvania], this is something the taxpayers paid for, this is something that was a huge part of many people's lives."

Patman says some owners have not taken kindly to finding photos of their properties on social media.

At one point, he says, NSW Police left a comment on one of his Facebook posts warning others about the illegality of trespassing on private property.

These days, he seeks permission first, and focuses on commissioned work.

One of his favourite projects was shooting what remained of the Terminus Hotel, in the Sydney suburb of Pyrmont.

It had been abandoned for three decades when a friend sent Patman an article about its impending sale.

He contacted the real estate agent and was granted access.

"And it was just everything I'd imagined," he says.

"It was like this pub that had just been lost in time."