Although the main wooden section of the house - which is now divided into seven flats - was built in the mid-1860s, before Firth took ownership, it was he who erected the tower in 1871 as one of the earliest concrete structures in Australasia. That has earned it a place on Heritage NZ's Category 1 list of historic places of special or outstanding significance or value, meaning any changes to the building should be strictly in keeping with its character.
Early photographs depict the building's commanding presence over a sparsely settled sweep of land down to the Waitemata Harbour before it was crowded in by successive generations of Aucklanders.
Josiah Firth, whose sons went on to found Firth Concrete, had a penchant for castles as he later built a slightly smaller version of his Mt Eden stronghold, which has since become a museum, in Matamata.
Marilyn Scott, one of the three doctors who bought the house in 1980, is selling the property while preparing for retirement.
"We used to have fantastic Guy Fawkes parties although I used to find it rather nerve-racking because of over-excited people in the tower."
Dr Scott said Suzanne Aubert of the Sisters of Compassion bought the property after Firth's death in 1897 and turned it into an orphanage. But the orphanage was eventually closed and by the 1920s the building lay derelict before being bought by the Garlick family, who divided it into flats after changing its main wooden section to a bungalow style while covering its verandahs.
Barfoot & Thompson agent Leila MacDonald is marketing the property as "an indescribable piece of New Zealand history".
