Old door keys have been dusted off and the attics cleared for the first time in nearly half a century.
Generations of accumulated "treasures" will be sold on Sunday in the first garage sale at the castle.
Gems for sale include an antique walnut bed, which was displayed in the castle for 35 years, a George Wood and Co organ, coach lights, a Victorian toilet, chairs, tables, furniture, cutlery and fabrics.
Castle managing director Norcombe Barker said the surplus items had been gathering dust for at least 44 years and had started to encroach on the administration area.
"It built up slowly over the years. We kept meaning to tidy it up, but we never got around to it; like most things," he said yesterday.
However, the selection was not without some controversy, marketing manager Deborah Price admitted.
"There were lots and lots of discussions about it. Everyone had a different interpretation of what was a treasure," she said.
"A lot of it is stuff left over from refurbishing the castle over the years. It was all around the place and after 44 years of competing for space it was time to clear it out.
"Larnach Castle was built as a family home, not for office managers and marketing managers and accommodation managers."
The mansion was built between 1873 and 1887 by banker, farmer, businessman and politician William James Mudie Larnach, who died in 1898.
In its heyday, the stately residence had 43 rooms and a ballroom, lavished over by a small army of 46 servants.
The sale and a family fun day will start at 11am on Sunday and includes a bouncy castle, buskers, magicians, horse-drawn carriage rides and a knights and princesses fashion parade.
