Twenty-five years ago, grieving the death of her partner, Carmel sold her house and moved from Queensland to Kalgoorlie, where she bought Questa Casa, the country’s oldest brothel. A clairvoyant told her she was going to buy a business thousands of kilometers away. “I can’t tell exactly what it will be,” the clairvoyant said. “It might be some kind of marriage guidance service.”

So Carmel left behind everything she knew and went into the sex industry, a trade she had no knowledge of or experience in. She maintains it’s the best decision she’s ever made.

A new documentary, The Pink House, takes us behind the scenes at Questa Casa, an unremarkable pink tin shed on an industrial street, as it struggles to remain relevant in a changing industry. Director Sascha Ettinger-Epstein delves into the history of the place (est. 1904) and the precarious circumstances it finds itself in today.

Prostitution has always been a big trade in Kalgoorlie, a former gold-mining town. Decades ago the streets were full of men every night. These days, Questa Casa is a shadow of what it was. Some nights no punters pass through the doors at all, and Carmel falls asleep at reception.

When I speak to Carmel on the phone she bemoans four nights in a row without a single paying customer. “Years ago we would have been open until daylight,” she says. “Times have changed.”

It’s Carmel’s charm that carries the film through its grimmer moments. Like when, preparing for the evening’s business, she takes to a selection of dildos with an electric duster. “As a matter of fact,” she says in her refined accent, “I imagine some of the blokes would like that.” And when she answers the phone and declines a customer’s unheard request. “No,” she says. “And you should be jolly well ashamed for even asking.”

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She’s a strict moral presence in a notorious profession. “I’m a mum figure,” she tells me. “They’re all somebody’s daughter. They’re all ladies.”

Carmel isn’t fazed by the sudden left-turn her life took. She came into it with a clean slate, not letting attitudes to prostitution cloud her approach. The film doesn’t moralise, either. Prostitution is murky territory, but it’s depicted with frankness and honesty. Carmel sees the brothel through a filter of romanticism, which never quite tallies up to the run-down tin shed that stands today. But as a film it’s not about the business, or even about the changing face of prostitution. It’s about one woman standing defiantly against the tide of time.

Carmel, now 80, is unashamedly nostalgic for the good old days of Kalgoorlie prostitution. She speaks fondly of when the Casa was overrun with horny miners, night after night. Now she runs a daily tour for grey nomads, telling bawdy stories of her decades in the business, from the one-legged prostitute (a surprisingly popular fetish, she says), to the punter who died mid-visit, and subsequently came back to life. She’s mythologised the Questa Casa’s past and tells its stories with flair.

So how did she respond to seeing her life on film?

“Quite frankly, I found it depressing,” she says. “I was hoping they’d show the happier times. But then everything went a bit bizarre.”

It did. The heart of the film is Carmel’s relationship with on-again off-again employee BJ, who struggles with drug addiction and becomes embroiled in a horrifying murder case. “BJ is a lovely girl,” she sighs, “but quite honestly, her brain is fried.”

When she first arrived at the pink house, BJ didn’t last long before she fell foul of Carmel’s strict no-drugs policy, and she was asked to leave. “She walked down the path and turned around at the gate and yelled ‘whoremonger!’” recalls Carmel. “I nearly fell over with laughter. What a wonderful expression.” Six months later, she was out of rehab, and turned to Carmel for help. “I gave her a chance,” she says.

“So many of these ladies take drugs, and think they’re cleverer than everyone else, that they know what they’re doing. When in actual fact,” she says politely, “they’re on the road to hell.”

Changing times mean an end to Questa Casa. By Christmas, Carmel plans to turn the business into a museum. BJ is coming back at Christmas – not to work, just to visit and relax. Carmel, and the Questa Casa, will live firmly in the past.

The Pink House will be screened a limited number of times in Australia in November and December.