It's a 4 hour flight from Melbourne to the north. Cairns is a tropical city (18 degrees south latitude) on the Coral Sea (where the famous WWII sea battle was fought). The Great Barrier Reef (GBR) begins 500 km south and Cairnes and runs 750km to the north.

We met our Cruise ship at Cairnes and cruised north toward the equator and into the reef.
There are thousands of uninhabited islands on the GBR and a few small towns (e.g., Cooktown) on the coast. The GBR is between 10 and 50km off-shore (as are the islands) so the only way there is by boat.The first Island we visited on the GBR is called Fitzroy Island. Deserted (except for us), it reminds you of Gilligan's Island --- a small island popping out of the ocean completely surrounded by white sandy beaches with mountainous, lush vegetation in the interior.
Barb and I standing on the beach with our boat anchored off shore. If you go 7,000 miles directly past the boat, you hit South America somewhere near Brazil (I think :-).
The weather on the GBR cruise was great -- all four days. We went to 2-Isles and Cooktown, where captain Cook (he was the first European to discover AU) first went ashore to repair his boat when it almost sank on the GBR. It's an isolated town of 2,000 people connected to populated Australia by an unpaveled road through the rain forest. We also spent time at Lizard island (some say it has the best snorkeling and diving in the word) and Ribbon Reef # 5 (which has the best snorkeling I've ever seen).

Every night we had beautiful sunsets ... here's a sample.
We have about 200 analog pics, many of them pretty good (if I do say so myself). We'll show 'em to you when you visit.

Bottom line ... it's a L O N G trip, but absolutely worth it. An experience of a lifetime.