Most people know that Queensland's Fraser Island is the largest sand island in the world and, in case you're interested, it's also Australia's fourth largest island after Tassie, Melville and Kangaroo.

But what you may not know - well, I didn't anyway -  is that there are two sorts of rock on this SAND island.

As we drove up the beach pounded by the Pacific on the eastern side, Chris, our guide on a Kingfisher Bay expedition, pointed out what appeared to be just plain old coastal rocks on the edge of the sand.

"That's 'coffee rock," he told us. "It's what lines the base of the perched lakes. Go on, pick some up and press it between your fingers."

We did, and it crumbled immediately, like a lump of dirt, which is what it is really, Chris told us. Just plant matter and sand compacted enough over a very long time to achieve a lumpy coffee-coloured rock-like appearance.

But further up the beach at Indian Head there were further surprises. Here were real rocks, 30 million-year-old ones that are the reason we now have a Fraser Island at all. Apparently they formed the pivot point that collected sand washing in from the ocean and like the grain of sand in an oyster shell, it grew from that.

So all is not as it seems here, which makes you view with suspicion the dead straight Seventy-Five Mile Beach which runs from North Spit in the south (I did tell you!) to Indian Head in the north.

"Reckon it was named by a fisherman," says Chris, dryly. "It's actually more like sixty-five." Which, at around 105 kilometres of beach edged by bursting surf and the more than occasional humpback sighting, is pretty impressive in any case.

The fact that it's also packed hard enough for buses and 4WDs to use as a road, tides depending (and, yes, you guessed it - it is a gazetted road with all the rules and regs associated with any highway) makes it easier to forgive the exaggeration.

Of course you have to watch out for other drivers, channels of water cutting across, and just when you have got used to that, there's a sign to remind you that you'd better also expect aircraft as Air Fraser Island uses the beach as a runway, dropping off people to join tours or take off on others for joy flights over the island.

Once aloft they will see even more amazing things - brilliant blue freshwater lakes dotting the bushland with massive trees, remnants from an early timber industry on the island, and patches of rain forest. Yes, that's another thing, Fraser reserves most of its sand for the beach and occasional 'sand blows' or dunes. All this and the island's two resorts at Eurong Beach and Kingfisher Bay.

Located on opposite sides of the island, these provide the major accommodation on Fraser. While many people bring their own 4WDs on a barge, or hire a vehicle on the island and then camp at the designated camping areas, others prefer to choose between backpacker accommodation, resort rooms or serviced villas.

In 1993 Fraser Island was declared a World Heritage Area (now one of just 400 in the world) a year after Kingfisher Bay Resort was completed. The resort was designed and built with dedicated respect to the environment and has won a large number of eco-awards.

It is so sympathetic with the environment that when arriving by boat from Hervey Bay, about half an hour away across the Great Sandy Strait, you make out the curved roofline of the main building only at the very last moment.

Once you have been bussed up to the reception area from the jetty, you see what a magnificent piece of work this is, as the hoop pine ceiling soars high above the entry, and Tasmanian oak stairs descend to the restaurants and pool area, giving a sensation of massive space and light.

But while this enigma of an island kept me deliciously off-balance for days - sand sculpted red 'pinnacles' could be in Central Australia, and people play golf on a beach unsafe for swimming (too many rips and sharks) - Fraser also won me.

Here are the pictures that live in my memory. A young dingo, one of around a hundred carefully ear-tagged, patiently posing for us. Champagne Rocks, a beachside swimming pool, and Lake McKenzie, each filled with splashing backpackers. Rainbows over the beach. And birds - a wedge-tail eagle flying high with a bandicoot limp in its talons, osprey, hawks, kites, seagulls, flying foxes, then on the beach, masses of black and white terns all facing the same direction.

Fraser is a place for everyone, and ideal for families. While the average stay for the 400,000 annual visitors is just a few days, there is enough to keep you happy for weeks. There's bushwalking, bird watching, 4WD ranger-guided tours, whale watching, fishing, dolphin search cruises, camping, photography, swimming, or simply hanging out at the resort relaxing by the pool or at the bar, playing sports, taking a champagne sunset cruise, enjoying a massage, or dining.

Pack an open mind when you come to Fraser Island, and be prepared to turn your preconceptions upside-down.

Words: ©Sally Hammond

Phootgraphs: ©Gordon Hammond