The house where the man and his daughter lived
Police in Amstetten, Austria, have described the cellar where a woman was allegedly held captive and sexually abused for 24 years by her father.
A series of underground rooms equipped for sleeping and cooking, and with sanitary facilities, lay behind a concealed door, police said.
The father, 73, allegedly had seven children with his daughter, now aged 42, and is under arrest.
Authorities are caring for the daughter and six surviving children.
The small town of Amstetten, about 130km (80 miles) west of Vienna, with its well-kept gardens is in shock, the BBC's Bethany Bell reports.
The case, she notes, is reminiscent of that of Natasha Kampusch, the Austrian teenager held captive in a cellar in a house in a Vienna suburb for eight years, who ran to freedom in 2006.
While police are not connecting the two cases, many Austrians are asking how such matters went undiscovered, our correspondent says.
Speaking on Sunday evening, Austrian police confirmed they had found the cellar where the daughter, named only as Elisabeth F, was allegedly held along with three of her children.
KEY FACTS IN CASE
Elisabeth reappeared at home after disappearing 24 years ago
Six children she says are hers have been found and placed in care
One of the children, aged 19, is seriously ill in hospital
Elisabeth's father Josef, 73, has been arrested on suspicion of incest and abduction
Three other children were adopted or fostered by the suspect, named as Josef F, while a seventh allegedly died soon after birth.
Police found the cellar after Josef gave them a code to unlock the hidden door, said Franz Polzer, head of the Lower Austrian Bureau of Criminal Affairs.
"There is not only one, but a number of rooms: one room to sleep in, one to cook, and there are also sanitation facilities," he said.
The floor is uneven and the hallway "very narrow" while the door is "very small", and one has to bend one's head to get through, he added.
"Everything is very, very narrow and the victim herself, the mother of these six or seven children, told us that this was being continually enlarged over the years," Mr Polzer said.
The area also contained sanitary facilities and "small hot plates" for cooking.
Elisabeth 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, after allegedly being hidden in the cellar with her mother and two siblings, sparked new interest in the whereabouts of Elisabeth.
When she disappeared on 28 August 1984, her parents had received a letter in her handwriting asking them not to search for her, and it was assumed she had run away from home.
However, according to Elisabeth's testimony to police, that day Josef had in fact lured her into the cellar, drugging and handcuffing her before locking her up.
Allegedly, he had already been sexually abusing her from the age of 11.
After Kerstin fell ill, doctors appealed for her mother to come forward to provide details about her medical history.
Josef then released both Elisabeth and the remaining two children from the cellar, telling his wife Rosemarie that she had chosen to return home, police say.
Police arrested him shortly afterwards and took the children into care, along with the three who had been adopted or fostered.
Rosemarie appears to have been unaware of the suspected crimes of her husband.
DNA tests are to be taken to establish whether Josef F was the father of the six surviving children.