For 24 years the daughter of Josef Fritzl and three of the children she bore him lived an isolated life in three tiny underground chambers, deprived of natural light and room to move around freely.
The rest of the Fritzl family lived in the house upstairs and had been forbidden by the domineering Josef Fritzl from ever going into the cellar, where the dungeon was.
The secret location was so well hidden that when the police searched the property they failed to find it until Mr Fritzl showed them where it was.
To get to the dungeon you had to pass through five different rooms in the cellar - including a room containing a furnace, a small office room and Mr Fritzl's workshop. Hidden behind a shelf in the workshop was a one metre-high reinforced concrete door.
The dungeon was entered via a narrow passageway leading into rooms that included a cooking area and shower facilities, with children's drawings on the walls. These rooms covered an area of approximately 60 sq m (650 sq ft).
The workshop and cellar area was strictly off limits to the Fritzl family members who lived upstairs.
Mr Fritzl sublet parts of the family house to tenants - who recall being forbidden to enter the cellar.
"Whoever enters it will be given immediate notice," one former tenant was told, according to the Austrian newspaper Kurier.
The secret door was electronically locked and could only be opened with a special code and a remote control - which Mr Fritzl is reported to have carried with him at all times.
The dungeon was divided into cells - some parts no more than 1.70m (5.6ft) high.
A narrow corridor, five metres long, led to an area which included cooking facilities and a small bathroom with a shower. The floor was uneven and bumpy. A tube provided ventilation.
Police said there were also two bedrooms - each containing two beds. At least part of the dungeon appeared to be padded and well sound-proofed.
Police refused to circulate pictures of the victims' sleeping areas or possessions to the press, saying they wished to protect their privacy.
Lack of oxygen
The rooms were described as being neat and tidy. There were no windows. The three children who lived in the cellar, a 19-year-old girl and her two brothers, aged 18 and five, had never seen daylight, and grew up with artificial light.
They had no fresh air and no room to exercise or run around. Hospital officials said the lack of oxygen may have contributed to the daughter's illness, which brought the whole case to light when Mr Fritzl took her to hospital. Police described the two boys as very pale, small and weak.
Children's paintings and posters were hung on the walls. Police say there was a television with a video player and a radio.
All of the seven children were born in the dungeon without medical supervision. One died shortly after being born.
As Mr Fritzl's secret family grew, he began to enlarge the dungeon. Police say it is still unclear how he managed to carry out this construction work secretly, as well as deliver food and clothing to his daughter and the three children without being noticed.
They believe the underground dungeon was originally one room, equipped only with washing facilities, which was gradually enlarged over the years. It is thought Mr Fritzl may also have expanded under the house's garden.
Amstetten authorities authorised the building of a cellar in 1978, city spokesman Hermann Gruber told the Austria Press Agency.
Mr Gruber said inspectors examined the project in 1983 - the year before Mr Fritzl's daughter went missing - and did not notice anything suspicious, but that he believed Mr Fritzl had not stuck to the original plans but had secretly expanded the cellar area.