Our first cruise stops At Airlie Beach, Yorkey Knob (Cains) and Port Douglas. Which of these ports is best for seeing the great barrier reef, and why? And is mandatory to do it through the cruise line, or is possible to do private excursions for this? I know that times in port are limited, and it seems like in this particular case, it may be better to go through the cruiseline. Also, what excursions would you recommend in the ports that you do not go to the GBR on, or would you visit more than one time? Thanks for all responses.