Sydney's South Head Heritage Trail is sublime window into Sydney at its best. One gets a sense of what the harbor must have been like when European settlers first arrived.
There are a number of benches or natural settings among the rocks or coastal shrubs that invite the would-be meditator. Avoid going on a weekend if possible, especially Sundays. On a typical week day there will be the occasional walker strolling past every five minutes or so but you'll have the place to yourself the rest of the time. Cicadas, song birds and the distant rumble of the surf make for a soundtrack of serenity if ever there was one.
It is Sydney, though, so you may have to contend with flies. Come with bug repellent, a fly head net or even a light shirt draped over ones face will do the trick.