Margaret Foster and Dr Graham Smith are sad to be saying goodbye to their 100-year-old Oyster Bay home, the only heritage-listed building in the suburb.
However, the couple are confident the new owners will love it as much.
"Whoever buys it will probably keep it for the next 50 years," Mrs Foster said.
The house, named "Deseret" at 2 Sage Road, was built over 10 years between 1920 and 1930 from cast concrete blocks, which were made by crushing sandstone from the area and mixing it with cement and casting the blocks in a mould.
The property is due to be placed on the market by Sanders Property Agents at Jannali in the next couple of weeks.
Sanders agent Nick Gleeson said the house was "part of Oyster Bay and Sutherland Shire history".
"I am sure we will have pretty much all of Oyster Bay here to have a look at the first open house," he said.
"We also expect to have a huge number of people coming from the eastern suburbs and the inner west.
"Our office sold a church in Como about 10 years ago and we had over 100 groups at the first open house and more than half were from those areas. We expect similar here.
Mr Gleeson said it was hard to price the property.
"It will have different value to to different types of buyers," he said.
"It's in fairly original condition, but they have maintained it.
"Because it is heritage listed, if you even want to paint or do anything with the wallpaper, you have to check with the council."
Mr Gleeson said he expected the buyer would be "someone who loves the history behind the home and loves the uniqueness that it brings.".
Dr Smith. a former ANSTO scientist, purchased the property in 1969.
He and Margaret Foster later married. Each had three children.
"It has been a wonderful home for our blended families," Dr Smith said.
Emma Dillon, said it was "a great place to grow up".
"I was very proud of it - and it was also across the road from the school, so I used to duck home for lunch".
The house was built by Robert Love for his wife Rose and their family, and originally consisted of canvas - which came from wrapping used on pianos shipped from England - which was then whitewashed.
Their daughter Enid McGuire told the Leader in 2002, "Dad found a machine at a home show that could make concrete blocks and he bought it for three pounds".
"He wanted to use coloured sand from rocks and Mum used to sit there forever and crack the stones into sand," she said.