The Chinese Garden of Friendship at Darling Harbour is a pretty spot where you see some greenery in the middle of the city. You can't entirely escape the city because the garden is small and you still get the city noise.

A large pond, the Lake of Brightness, in the center of the garden provides a view for the lovely circle windows everywhere and the tea house. As you walk to the back of the garden, you traverse an incline, pass a roaring waterfall, and reach a little forest with a red pavilion with distinctive roof. Stay a while and watch the breeze rustle the branches. On the southern side, there is an interesting cluster of stacked boulders in the shape of famous characters. Walk quietly along the pathways and you'll see giant lizards, so ancient and strange. There is also an assortment of birds that tread happily around the edges of the pond, and carp that swim leisurely up to its shores. It's weird to look up and see the city skyscrapers.
This garden didn't really make me stoked like other gardens, but it was a pleasant diversion that takes less than an hour.
While you're at Darling Harbour, don't miss the Sydney Aquarium, which is marvelous. Watching the dugongs will make you so happy! Wild Life Sydney Zoo is also a good place to visit, where you can see koalas and kangaroos in large enclosures.
For more Chinese culture, walk a short walk south to Chinatown and get some great souvenir shopping done at Paddy's Markets.

Directions

Chinese Garden of Friendship is located at Darling Harbour, 38 Harbour Street, Sydney NSW 2000, Australia, call (02) 9240 8888.
You can catch the light rail (tram) to the Chinese Garden of Friendship. Get off at Exhibition or Paddy's Market, and it's a short walk to the garden. If you get off at Paddy's Market you can buy some australiana souvenirs while you're there.
Hours are 9:30-5:30 daily (closes at 5pm Apr-Sept). Closed on Good Friday (friday before Easter) and December 25. Cost to enter is $6 for adults and $3 for children.

Click on map for interactive view