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. Investigators recently discovered another door to the dungeon prison, which was blocked by a 500-kilogram (1,100-pound) steel and concrete door that Fritzl probably stopped using when he later constructed an electronic door for a second entrance, Polzer said.Investigators recently discovered another door to the dungeon prison, which was blocked by a 500-kilogram (1,100-pound) steel and concrete door that Fritzl probably stopped using when he later constructed an electronic door for a second entrance, Polzer said.