Australia

Take a dive at the great barrier reef. Even if you've never done it before, they have introducory dives. There are some big fish. If you take a throwaway underwater camera, beware that you can probably only take one picture as the shutterbutton will not come up anymore after you press it because of the pressure underwater.
If you don't have much time in Australia but still want to see kangaroos, go to the zoo in Brisbane, they've got plenty.