http://news.bbc.co.uk/2/hi/europe/7373172.stm
i don't see how the cellar extended to under the backyard, beyond the house. then again this isn't a very clear map.
still..... after 24 years.. not a few weeks, months, or a few years, or 10 years.. but TWENTY-FOUR years.... (!!!!) you would think a little light would go on inside that woman's head and she might wonder.. 'hhmmm...... what IS he doing down there all this time, anyway??' typically your common sense and curiosity would tell you that someone who was SO adamant about his secrecy.. was up to no good. especially if they are an evil tyrant like him!
i suspect that she was probably happy when he was gone, & didn't care so much where he went.. because she could have the house (and children) to herself, and the toxic atmosphere he brought into a room was less oppressive.
but STILL........ twenty fours YEARS....???? AND with a 'missing' daughter on top of it?? and the rape/abuse being an 'open family' secret?? AND the fact that your husband served jail time for raping a stranger??? you would think she might wonder if his frequent trips to the basement might have something to do with his daughter's disappearance, that he was hiding something bad, etc.
most women can detect subtle signs that their partner has been with another woman... in his behavior, speech, attitude, and with all 5 (and sometimes, 6) senses. i know this man & his wife were no longer close,, but don't anyone tell me she didn't have some inkling that something strange was going on in that house.
you would have to be very mentally slow, or even retarded, to be completely unaware or anything at all, for so many years.
another question.... what about the ventilation pipe that he installed? where did that lead to? wouldn't you be able to hear voices echoing up through the pipe, the sound of TV/radio, etc, coming out from underground? nothing has been said about this. also, if the daughter knew he was going away for a month, you'd think they would start screaming for help. but he had them so paralyzed by fear, i can see how they might be too scared to do anything.