If you get the chance, I highly recommend going on a cruise on the Sydney Harbour.
There is something magical about this. It is hard to put a finger on it. But on a warm summers night, cruising around the harbour and sipping on a beer or wine, while talking to other guests, is pretty hard to beat.
You get to see the city and its waterfront in a completely new way, and it is unfortunate that more people don't take up this experience.
Watching the sun set over the horizon and the city lights start to come on while gently rocking on a cruise boat is beautiful. Do it if you get the chance!