People – It is permissible to photograph anyone in a public space. Thus if you see a celebrity and poke a camera in her face you can point out to the 150kg gorilla in a suit and sunglasses accompanying her that it is your legal right. You might explain that in Australia there is nobody has the right to not having their photo taken in a public place and that while it is legal for him to block your view he may not confiscate your camera or memory card without a court order. He will say that he is glad that he had this conversation and that your logic and persuasive reasoning has convinced him of your rights in this case. In general in Australia there is no such thing as a person having a right not to have their photo taken in a public place.
Buildings & monuments In general, any buildings or monuments visible from a public place can be photographed in Australia
Anything visible from that public place – this includes the visible parts of public and private properties and anything happening there. This contrasts with, say, France, where you may find it is not permitted to photograph a prominent building even though it is clearly visible through the fence when standing on the footpath.