get to the prison . `` You would have to open up a total of eight doors , and ... -LRB- for the -RRB- last door which would go into this space -LRB- where the family was imprisoned -RRB- , you would also have to use electronic opening apparatus , '' Polzer said . `` We will have to find out perhaps later from now if perhaps there are other spaces we have n't discovered yet , and perhaps maybe there is something else interesting . '' Fritzl was recently arrested and confessed to holding his daughter , Elisabeth , captive in the dungeon under the Fritzl home for decades , repeatedly raping her and fathering seven children -- six of whom survived . Three of the children were adopted by Josef Fritzl and his wife after he concocted the ruse that Elisabeth had left the babies on their doorstep . The story of the family 's imprisonment began to unravel more than two weeks ago , when one of the children still in the dungeon , 19-year-old Kerstin Fritzl , fell seriously ill with convulsions . The father agreed to take her to a hospital , the first time
-LRB- CNN -RRB- -- Austrian investigators Monday released more details about the elaborate underground cellar where Josef Fritzl kept his daughter imprisoned for 24 years , along with three of their children . Josef Fritzl admitted to authorities he raped his daughter and fathered her children . Investigators believe Fritzl planned to build the cellar as early as 1978 , shortly after , according to his daughter , he began raping her at age 11 or 12 , said police spokesman Franz Polzer . The 73-year-old Austrian began building the dungeon as part of an addition to his home that year , and simply added the hidden space -- which was not recorded in any building plans -- Polzer said . It took Fritzl until 1983 to finish the addition , Polzer said . Investigators recently discovered another door to the dungeon prison , which was blocked by a 500-kilogram -LRB- 1,100-pound -RRB- steel and concrete door that Fritzl probably stopped using when he later constructed an electronic door for a second entrance , Polzer said . Fritzl , who police believe was the only one with access to the cellar , had to travel through an elaborate maze to