Police in Austria have entered a cellar where a man allegedly held his daughter captive for 24 years, during which time he may have fathered seven children by her.
The basement area consists of a very narrow hallway and several rooms, said Franz Polzer, head of the Lower Austrian Bureau of Criminal Affairs, on Austrian TV.
Authorities accessed the area after the father told them how to unlock a hidden door using a code only he had known.
Now aged 42, the woman was found after a tip-off to police. Her 73-year-old father Josef Fritzl has been arrested and is being held in custody.
"But it also means the father is talking to police."
The youngster, 19-year-old Kerstin, was said by police to be "gravely ill".
During the 24 years that followed, she said she had six children by him.
The two oldest children, aged 18 and 19, and the youngest aged 5, had been locked up with their mother since birth and had never seen sunlight or received any education, police said.
Police said Elisabeth only agreed to talk after the authorities promised she would not have to have see her father again and the children would be taken care of.
The mother and children are now being treated in hospital by a team of psychologists.