Fitzroy Island is larger than Green Island. It is also a national park that offers good snorkelling. There are also a couple of hiking trails on the island and also some good beaches.
Fitzroy Island is about the same distance from Cairns as Green Island, but it is less crowded, cheaper to get to and a more popular destination among backpackers.
Coming & going
The Fitzroy Island Ferry takes 45 minutes to sail from Cairns to the island. The return trip costs $72.