Sometimes just getting out to the reef is an adventure, especially if you travel by helicopter or seaplane. Once you get there, the undersea views vary greatly, but even in the shallower or murkier spots you'll still see creatures you'd never otherwise encounter outside an aquarium, or a fancy fish tank. In prime viewing spots along the outer reef, and especially around Orpheus Island, the variety of coral and fish is incredible, and well worth the price you'll have to pay to access it.
There are thousands of spectacular dive sites scattered along the coral spine of the Great Barrier Reef. Some of the most famous, like Briggs Reef off Cairns, draw hundreds of divers and snorkelers a day with clouds of fish and coral formations, along with moray eels, stingrays, and the occasional white-tipped reef shark. More remote dive sites, like those in the far north of the Coral Sea, are only accessible after a weeklong journey by live-aboard dive boat.
Life in and around the water is why most people visit the Great Barrier Reef, but flora and fauna on the islands themselves can be fascinating. Some have rain forests, or hills and rocky areas, or postcard-perfect beaches. On Heron, Wilson, Lady Musgrave, or Lady Elliott, see green and loggerhead turtles flip-flop ashore to lay their eggs November through March. Lady Elliott and Heron islands are known worldwide for nesting seabirds, and migrating species stop in at by the thousands July to September.