Our minibus barrels beyond Maroubra towards Botany Bay with our instructor, former Royal Australian Navy ship diver Robert Ridge, behind the wheel. In the back are two English lads, flashing enough gold and tattoos to rival the markings of a tropical fish. As we near Bare Island, they chat to us about the mother country and the meaning of the word "pukka".

Dubbed "bare" by Captain Cook, the island was once used as a garrison. More recently, it served as a set for Mission:Impossible II. Ridge says this place is one of Sydney's top five dive sites.

Before exploring the depths, we beginners are handed a form that asks, among other things, whether we are pregnant. Then it's time for a briefing on a bench beside an empty snake-show pit. The talk is interrupted by a stranger who looks like a bandit from Mad Max. He wanted to make sure us "blow-ins" don't cause an obstruction, adding: "Captain Cook was the first blow-in and look what happened to the feckin' Aborigines!"

After humouring the crank, who duly disappears, Ridge introduces some drills and teaches us scuba's simple sign language. Next, we strip and squeeze into our wetsuits and slipper-like "boots", stashing our belongings in the minibus safe.

My tank-clad wetsuit gives me armour-like confidence that dwindles onc ewe step into the Pacific's chilly waters for some drills. The "partial mask flood and clear" exercise, which makes me think of trench warfare, requires the diver to submerge, prise the top of their mask open a crack then snort the water that leaks in back out through the bottom.

As Ridge does a demo, my nervous brain fogs over. When my turn comes to perform the manoeuvre, which the English boys manage easily, I gulp water and gag, tasting a faint trace of vomit. Only after several more attempts do I get it right to Ridge's satisfaction.

Before we go under, Ridge teaches us how to control our breathing. Like driving, scuba is all about keeping cool and never making mistakes.

Then it's time for the plunge. We follow our guide, rarely venturing deeper than a few metres underwater. It's a great feeling, not needing to surface to draw breath - unlike those snorkellers, reviled as "bubble watchers" by scuba devotees.

In one edgy moment, one of the British lads accidentally snags the hose of my regulator, forcing me to bite my mouthpiece harder. Otherwise, aside from guilty feelings about occasional encounters between the coral and my flippers' tips, I am happy.

I can just about see why the French aquatic TV star Jacques Cousteau wrote: "From birth, man carries the weight of gravity on his shoulders. He is bolted to the Earth. But man has only to sink beneath the surface and he is free. Buoyed by water, he can fly in any direction - up, down, sideways - by merely flipping his hand. Underwater, man becomes an archangel."

Alas, the angelic antics only burn up to about 350 calories an hour - roughly a third as many as windsurfing. That's because in the water, buoyancy removes the need to exert yourself physically, other than waggling your flippers.

As we drift above sponge beds and kelp fields, we keep an eye out for the marvels Ridge has described, not least the "weedy sea dragon", a surreal relation of the seahorse that hangs out exclusively in southern Australian waters. I don't find one, but I do register the blue bulk of an eastern blue groper. I hold out my hand and it darts out of reach, then circles our group. The curiosity is mutual.

The next creature that swims into view is a stonefish, all lips and poisonous spines. It has rather less time for the rubber quartet invading its space and, like any decent villain, dodges past us before vanishing into the shadows. The bullseye fish live up to their name, their sail-like bodies embossed with giant eyes that make them seem incredibly spooky.

Other sights include bluebottle jellyfish, fleshy starfish, a pair of sea slugs and a Port Jackson shark egg. Normally found wedged in a ledge, the one we see in the medium visibility spins, eludes our grasp but captures our attention, eerily perfect in its form ... pukka.

Now you try it

Let's Go Diving, 44 Great North Road,Five Dock, 9713 4108 or

www.letsgodiving.com.au.