I remember going to Kavos as a young kid (19ish) and that was pretty cool. The only thing that was a bit offputting was the open sewerage systems...
I'm biased but I would have to say the Ionian islands are the best group. Very lush, Mediterranean climate and lots of culture.
reef trips from Cairns are a very popular way to see the Great Barrier Reef. It's pretty good value as well.
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