It may surprise most Sydneysiders but this city is home to the country’s biggest urban park. To get a sense of the size of Western Sydney Parklands, imagine this: a space 14 times bigger than the Royal Botanic Gardens, the Domain, Centennial Park and Moore Park – combined.

The parklands span 5280 hectares across three local council areas – Blacktown, Fairfield and Liverpool – created over the years as successive state governments put aside open space, abandoned farms and to create a 27-kilometre corridor of green space among western Sydney’s urban sprawl.

It’s an impressive example of government forward planning – the process started half a century ago.

And to celebrate Western Sydney Parklands 50th birthday there’s a bunch of planned events, and most are free.

There will be astronomy tours (July 28 and August 4) led by Wiradjuri woman and astronomer Kirsten Banks. It takes place at The Dairy in Abbotsbury, about 45-kilometres west of the CBD – an ideal location for stargazing because there’s not much light pollution.

Fitness fanatics can test their might on the Spartan Workout Tour (August 4), a series of six 20-minute workouts, also at The Dairy. (It’s free, but participants must register in advance.)

There’s also native-tree planting on August 4, bird watching on July 28, and special deals from TreeTops Adventure Park and the Skyline Drive In in Blacktown.

“We really wanted to get the word out to people who might not know about it,” says Joanna Savill, director of business development for Western Sydney Parklands, of what she thinks is one of Sydney’s best-kept secrets.

The 50th birthday festivities will run until August 4 at Western Sydney Parklands. See the full program here. Some events require bookings.