By Phil Mercer
BBC correspondent in Sydney
Melody O'Gara has been missing for more than three weeks
The disappearance of a young British tourist in Sydney more than three weeks ago continues to baffle Australian police.
Melody O'Gara, 28, from Bolton, was last seen at a friend's house near Bondi beach.
There's been no sign either of Melina Daubl, an Austrian teenager, who went missing in Sydney around the same time.
Detectives do not believe the two cases are connected but these mysterious disappearances have highlighted the darker side to travel in Australia.
"It's your world's worst nightmare," Melody O'Gara's father Hugh told the BBC in Sydney, where he's helping the police inquiry.
"Nothing that I've ever gone through before compares to the roller-coaster I'm on now," he said.
Investigators believe that Melody, who was in Australia on a working holiday, may have committed suicide after her handbag was found on the edge of a cliff near Bondi beach.
Her disappearance has caused unease among some British backpackers in Sydney.
"My mum back home is out of her mind worrying about me," said Sam, a student from Hampshire.
"We're all making sure we're not out late on our own while we're here."
At the end of October, a 52-year-old holiday-maker from Cumbria was found dead on a dusty track in the outback.
The body of Ethel Hetherington was discovered near an Aboriginal community, several kilometres from her hotel at Uluru, formerly known as Ayers Rock.
An accurate picture of what happened to her and why has still to emerge.
One theory is that she was invited to the indigenous settlement and died from heat exhaustion when she tried to walk back in searing desert temperatures.
Family and friends have been distributing these missing posters
Tragedies and mysterious disappearances are clearly not good for Australia's international reputation.
Tourism is a multi-billion dollar business. However, such unforeseen events don't appear to have scared off many overseas visitors.
"Australia is still a very safe destination," Alan Collingwood from the Travellers Contact Point in Sydney told the BBC News website.
"Australia is probably considered a softer option compared to going to South America and South Africa.
"Young people want to have adventure and if there is any criticism of Australia is that it's seen to be a little soft in that area."
There have been a number of notorious backpacker murders and mysteries over the past decade.
In 1996, Ivan Milat, one of Australia's most notorious serial killers, was jailed for life for killing seven young travellers, including two Britons.
Melody O'Gara's handbag was found near a cliff-edge close to Bondi beach
Four years ago, 15 backpackers died when an arsonist attacked an old wooden hostel in the farming town of Childers, in Queensland. Among the victims were seven tourists from the UK.
A few kilometres down the road in Bundaberg, Caroline Stuttle, a gap year student from York, died after being deliberately thrown off a bridge during a robbery.
In the Northern Territory, a man will face trial next year accused of killing the British tourist Peter Falconio, who disappeared in the Outback in July 2001.
Such incidents are rare but they inevitably make the headlines.
Despite these highly-publicised deaths and disappearances, Australia retains a frontier feel that will continue to attract legions of visitors from overseas.