So why has a crowd of 20 or 30 people chosen to perch on folding chairs, mugs of weak milky tea balanced on their knees, in a rather Spartan room with nothing but a slide show and a lean Irishman with a fanatical gleam in his eye by way of diversion?

The Irishman stalks back and forth across a low plywood platform. He leans forward; he crouches; he stretches tall. His voice ranges from tent revival preacher boom to Monty Python lunatic screech as he veers from thundering pronouncements to the high-pitched tone he uses to talk about the "teeny-tiny microscopic animals" who built the titanic wonder we've all come to this remote place to see: the Great Barrier Reef.

The reef is a Mecca of sorts for scuba divers. I've traveled all the way from New York, spending almost 24 hours on or between planes, to get here. More experienced diver friends were silent for a few moments when I'd told them where I was going -- did they think the trip would be wasted on me, a mere novice and someone likely to spend most of my underwater time fussing with my mask, equalizing the pressure in my ears and double-checking my air gauge?

The reef, as Paddy Colwell, the Irishman, reminds us, is enormous. Its area is larger than that of Great Britain, half the size of Texas, and it's visible from the moon. Every bit of it was created by those teeny-tiny microscopic creatures, the animals that make up the myriad varieties of coral. Colwell reminds us several times, pinching up a fold of skin from under his tricep, that "plants live in the flesh" of those animals, a statement that never fails to send an unpleasantly prickly shudder down the back of my neck. All very well for the coral, which thrives in a symbiotic relationship with those plants, but the thought of it gives me the creeps.

This is only my second scuba-diving trip, and I am sorely in need of Colwell's teachings because I made my inaugural dives in Hawaii. However impressive the Great Barrier Reef may be in theory, when you're diving, the most you can see of this discernible-from-the-moon structure is the patch immediately in front of your mask. And unlike the dive spots in Hawaii -- where we could hardly turn around without tripping over moray eels, octopuses, sea turtles, rays, shrimp, dolphins and hallucinatory clouds of bright butterfly fish -- the parts of the reef I've visited so far seem relatively underpopulated.

What I need to do, as Colwell explains, is look closer, look slower and look smarter. He passes around the chalky skeletons of various corals, teaching us their names: brain coral, staghorn coral, boulder coral, fan coral, all of which, in a rare example of typological good sense, look exactly like the things they're named after. He explains that if you wait patiently by a pockmarked specimen of brain coral, the tubeworms you frightened into hiding with your typical, blundering human approach will reemerge. The worms live in burrows right in the brain coral (another prickly shudder at that one), but they stick out their frilly heads to sweep tiny microscopic food particles from the water.

Colwell, a marine biologist and a native of Dublin, later tells me the eventful, if somewhat confusing, story of how he came to be doing an educational slide lecture called Reef Teach six nights a week in downtown Cairns. It involves teaching high school biology students in Ireland and ex-prisoners in Boston, diving with BSAC (British Sub-Aqua Club) in "zero visibility bog lakes in Ireland," taking a courier flight to Melbourne, trying to open a pub in the Outback, discovering he'd lost all his savings through an investment outfit called a building society, driving backpackers around in a van and becoming a dive master in Queensland where he quickly grew outraged at the divers' lack of sound marine biological knowledge. His narrative is laced with what are no doubt well-grounded diatribes against tour operators, marine park administrators, agribusiness, ecotourism and, understandably, building societies.

One by one Colwell can testily count off the common misperceptions burdening visitors to the reef. They think that sharks must keep moving or they'll die. They think that giant clams live to be 200 years old ("ridiculous!") and will clamp down on the extremities of divers until they drown. They think that barracuda are dangerous to humans. In fact, most of the creatures people assume pose a threat to divers -- sharks, manta rays, giant clams, barracuda -- are harmless. The waters off tropical North Queensland do contain their share of deadly nasties, but these tend to be decidedly unglamorous: the venomous box jelly fish, the stone fish, the pretty little cone shells that you must never, ever pick up.

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