A 73-year-old Austrian, Josef Fritzl, from the town of Amstetten, has confessed to imprisoning his daughter in a cellar for 24 years and fathering her seven children, police have said.
In 1984, police say, he drugged and handcuffed Elisabeth and locked her in the cellar. During her 24-year imprisonment, Elisabeth gave birth to seven children, including twins in 1996 - one of which died.
Police have released photos of the cellar in which they were kept. They show a concealed network of windowless chambers. The rooms were equipped for sleeping and cooking, and with sanitary facilities.
Elisabeth, now 42, is receiving medical and psychological treatment and her children are in care, police said. Her eldest daughter, Kerstin, is in hospital with a serious illness.
The 19-year-old's admission to hospital a week ago sparked new interest in the whereabouts of Elisabeth and eventually led police to question her and arrest Mr Fritzl.
Among the neighbours, who police have said knew nothing, there is a sense of shock and disbelief. "You just can't imagine this happening here, in quiet Amstetten," one woman told the BBC.
It is the third case involving people being locked in cellars to come to attention in Austria in recent years. Two years ago a young woman, Natascha Kampusch, escaped after being held for eight years.