Parramatta Open debuts with access to historic sites including Australia's oldest public building

Some of Western Sydney's most interesting and historic sites, including Australia's oldest surviving public building, will be unlocked to the public for one day.

Parramatta Open will make its debut on Saturday, offering visitors rare access to 16 buildings and spaces that are normally off limits to members of the public.

The one-day event is the first extension of the long-running Sydney Open, and manager Tania Quax said there had long been ambitions to expand the program beyond Sydney's CBD.

"So Parramatta was the obvious choice, really. It's got the heritage and the history, but it is also one of the fastest evolving parts of Sydney," she said.

"That gives us a lot scope to find really good buildings."

One of the major drawcards of Parramatta Open is the UNESCO World Heritage-listed Old Government House, a rare time capsule of Australia's convict past.

Constructed between 1799 and 1818, the convict-built house was the country residence of 10 early New South Wales governors and is the nation's oldest surviving public building.

Mark Ransom, who has been a volunteer guide with Sydney Open for about a decade, will be running the tours at Old Government House.

Curious visitors become volunteers

Another volunteer, Khadija Ibtisam, who has a background in architecture and design, came on board in more recent years after being a regular visitor at Sydney Open.

She will supervise tours at Parramatta Female Factory, the first and only surviving purpose-built site for female convicts in Australia.

In the early 1800s, thousands of women and children passed through the complex, which served as a prison, hospital and asylum.

"It's not just about the history of these built environments, it's also about the lives that were affected within these buildings," Ms Ibtisam said.

The public will also get access to Elizabeth Farm, the nation's oldest surviving colonial homestead, along with modern buildings like PHIVE and the 55-storey 6-8 Parramatta Square tower.

In an early indicator of its popularity, tickets have sold out ahead of the event.

Nadine Johnston, who manages Old Government House in her role with the National Trust of Australia, is among those planning to attend the festival.

"Personally, I'll be taking a day off and going around to the other properties, so it'll be excellent," she said.

"In this local government area there's over 120 historical sites, so there's a lot to learn."

There are plans to make the satellite event an annual feature of the Sydney Open program, with the location of next year's instalment yet to be announced.

The Sydney Open flagship event will take place in Sydney's CBD on November 1.