One long established and very lovely guerrilla garden in Sydney is in Lavender Bay, a short walk from Milsons Pt railway station and ferry wharf.
It is between the house where Wendy Whiteley lives, and the railway below. When she first moved in, with her husband Brett and daughter Arkie, the site was a rubbish strewn embankment, with car bodies and weeds. The land is owned by the railway.
It is now a splendid oasis of greenery, with charming bowers and picnic tables, a maze of paths, and lots of lovely sculptures. The city skyline and the Sydney Harbour Bridge are in view, or just out of view, according to your preference.
I recommend it as a picnic venue. There are no fences or gates, it is open. A few signs prompt the visitor to clean up after themselves.
The ashes of Brett and Arkie are scattered in there, somewhere.
Pictures of this and of the Maori fellow's garden in Kings Cross, as well as many of the TV funded guerrilla gardens of late, are here -http://www.flickr.com/photos/25063581@N08/sets/72157612369130045/
If anyone knows of any more guerrilla gardens in Sydney, please tell me, and I'll take more pictures to display there, and also here -http://www.flickr.com/groups/479008@N21/