Josef Fritzl – who fathered seven children by raping his captive daughter in a dungeon – had a secret basement in a guesthouse he used to own.
Construction workers unearthed hidden areas while measuring the property in the lakeside town of Unterach am Mondsee in Austria.
Fritzl ran the Seestern before leaving in 1996 for Amstetten, where he would rape daughter Elisabeth more than 3,000 times in a sound-proofed dungeon.
An anteroom with a staircase leading nowhere was discovered behind a wall during the inspection, which was required due to the former guesthouse never receiving a building permit.
It is now rented by a man known only as Helmut L, who said: ‘There are cavities everywhere in the house.’
The property burned down twice during Fritzl’s stay, leading police to investigate him as a suspected arsonist.
According to local media the Seestern was never properly inspected by police even after they learned about Fritzl’s crimes in his next property.
Fritzl’s house in Amstetten was bought by Herbert and Ingrid Houska for only €160,000 (£143,581).
They renovated the building, which includes multiple flats, and have rented out all 10 of the spaces.
Herbert Houska said he saw the refurbishing of the house was like burying a coffin.
‘The sarcophagus of Amstetten is gone,’ he said.
‘I think really something beautiful has emerged and the past has been buried.
‘Many residents congratulate me and are happy.
‘It is time to finally look forward.’
Only the basement of the complex where Elisabeth was held is not in use as the Amstetten authorities filled it in to prevent it from becoming a shrine to other perverts.
When Fritzl owned the house none of the tenants knew about the tragedy that was playing out beneath them in Fritzl’s self-constructed dungeon.
The Josef Fritzl rapes, revisited:
Fritzl’s abuse of daughter Elisabeth started when she was just 11 years old and he kept her captive in a dungeon he constructed for 24 years, raping her thousands of times.
To explain her disappearance, he told people she’d joined a cult.
He fathered seven children with Elisabeth, one of whom – called Michael – died shortly after being born.
Three others – Lisa, Monika and Alexander – were raised by Fritzl in the family home, after he told social workers the infants had appeared on his doorstep.
The remaining three – Kerstin, Stefan and Felix – were kept in the dungeon and threatened with gassing if they tried to escape.
But in 2008 Kerstin went into a coma and Fritzl took her to hospital, where her rotting teeth and malnourished state alarmed doctors.
Fritzl allowed Elisabeth to visit her daughter in hospital, where she was arrested and exposed her father’s horrific crimes.
He is serving life in Austria’s most secure psychiatric prison for murder and rape.
The murder charge relates to the death of Michael, which was caused by negligence.
In May Fritzl changed his surname to Mayrhoff in a bid to avoid identification by other prisoners.