In Poland, crowds solemnly file into the Auschwitz-Birkenau concentration camp, where the iron gates are inscribed with the words "Arbeit macht frei" (work sets you free).

In Sydney, there are sightseers entering Hyde Park Barracks where convicts and then the destitute were held many years ago.

What links these sites, apart from their depiction of some of life's saddest, baddest and maddest moments, is that each is part of a phenomenon that is reportedly growing around the world. Dubbed "dark tourism" by academics who are starting to focus on it, the trend reflects a fascination with places or exhibitions that are mounted around themes of suffering, trauma, death and punishment.

In Australia, academic Dr Jacqueline Wilson says dark tourism attracts at least 1 million people a year. "Hundreds of thousands visit places such as Port Arthur, Fremantle Prison, Old Melbourne Gaol and Hyde Park Barracks, and if you add them up along with all the other dark tourism sites, it totals more than a million visits around the country," the University of Ballarat lecturer says.

Dr Wilson, author of Prison: Cultural Memory and Dark Tourism and one of the few to seriously study it in Australia, says dark tourism here is focused on prisons. But there are other places, too.

"At Darwin's museum there is a cyclone Tracy room where people can listen to the sound of the wind that was recorded on the night of the cyclone. It is one of the most ear-piercing and eerie things anyone has ever heard. It's about suffering and trauma and loss."

It may be fascinating, but is dark tourism ethical? Dr Wilson says that, on the whole, people visit out of a sense of social engagement rather than simple voyeurism.

"We can all do with seeing that side of life as long as we are not getting our kicks out of it," she says. "I've interviewed thousands of tourists at these sites, and I'd say that most people who visit are well motivated.

"Dark tourism sites are of tremendous importance in terms of understanding our society. People who go to them feel deeply and may be aggrieved. Some are looking for redemption or explanation."

But, she acknowledges: "There's also the flip side of the fascination of the macabre, which I think we all have in us."