BBC News

has a diagram of what the chamber of horrors looks like, as the authorities have found it:




The mystery is that as the second family grew, how Fritzl was able to expand the cellar in secret. The area is about 650 square feet (60 square meters), about the size of a small apartment but downright claustrophobic for four people. It is somewhat larger than my apartment, which is 500 square feet.

It has been noted Fritzl was granted the right to build a cellar in 1978, and it was examined in 1983, the year before Elisabeth was abducted. However, no one noted anything suspicious.