Sun, a sandy beach and a nice view. Is that what all tourists want? Not quite. Trips to sites of death, brutality and terror are on the increase. About 350,000 people now visit Robben Island in South Africa every year. That's where Nelson Mandela was imprisoned for 18 years. The prison was closed in 1996 and is now a so-called 'dark tourism' destination.

This trend has intrigued researchers at the University of Central Lancashire, which has even created an Institute for Dark Tourism Research. They examine why people feel compelled to visit places like Auschwitz in Poland or New York's Ground Zero. Is it just a case of morbid fascination?

Director Philip Stone says his research suggests that visitors want to find some kind of meaning in these places of suffering. They try to empathise with victims and imagine the motivations of the perpetrators, he says. Then they have a sense of relief that they can step back into the safety of their own lives.

And what appeal could Chernobyl, the site of a catastrophic nuclear accident in 1986, have? Stone says such grim places make people face their "own mortality". In a culture that usually removes death from the public domain, these destinations are strongly associated with loss of life, he says.

And yet this kind of activity has a long history, according to Stone: "It's always been there. You could say that a medieval execution was an early form of dark tourism."

The researcher, who worked in the tourism industry before becoming an academic, also pointed out an example of dark tourism closer to home. In Pendle in Lancashire in the 17th Century 11 people were charged with murder by witchcraft.

"Four hundred years ago they were innocent people who were killed. Now they're a tourist destination," says Stone.

What about you: would you visit the battlefields of World War I and II or the former prison of Robben Island?