Our minibus barrels towards Botany Bay with our instructor, former Royal Australian Navy diver Robert Ridge, behind the wheel. In the back are two British 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 James Cook, the island was once used as a garrison. More recently, it served as a shooting location in Mission: Impossible II. Ridge says that, well within the city limits and not far from the airport, the island is one of Sydney's top five dive sites.
Before exploring the depths, we're handed a form that asks, among other things, whether we're pregnant. Then it's time for a briefing on a bench beside an empty snake-show pit. It is interrupted by a stranger who looks like a bandit from Mad Max. He tells Ridge to make sure we 'blow-ins' don't cause an obstruction, adding: 'Captain Cook was the first blow-in and look what happened to the Aborigines!'
Ridge introduces some drills and teaches us scuba's simple sign language. Next, we strip and squeeze into our wetsuits, stashing our belongings in the minibus safe.
My tank and wetsuit fill me with confidence, but it disappears as I step into the chilly Pacific for drills. The 'partial mask flood and clear' exercise, which for some reason 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 demonstrates, my nervous brain seizes up. When my turn comes to perform the manoeuvre, which the British boys manage easily, I gulp water and gag, tasting a trace of vomit. Only after several further attempts do I do it to Ridge's satisfaction.
Before we go under, Ridge teaches us how to control our breathing. Like driving, scuba is all about keeping your cool and not making mistakes.
Then it's time for the plunge. We follow our guide, rarely venturing deeper than a few metres under water. It's a great feeling, not needing to surface to draw breath, unlike those snorkellers, dismissed as 'bubble watchers' by swaggering scuba types.
I'm startled when one of the British lads accidentally snags the hose of my regulator, forcing me to bite my mouthpiece. But aside from mild guilt when the tips of my fins brush the coral, I'm happy.
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 relative of the seahorse that inhabits southern Australian waters. I don't find one but I do register the blue bulk of an eastern blue groper (left).
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 rubbery quartet invading its space and, like any decent villain, dodges past us before vanishing into the shadows. The bull's-eye fish live up to their name, their sail-like bodies embossed with giant eyes that make them spooky.
We also spot bluebottle jellyfish, fleshy starfish, a pair of sea slugs and a Port Jackson shark. They're normally found on submarine ledges; the one we see in the medium visibility spins and eludes our grasp, but captures our attention with its eerily perfect form. Pukka.
For more information, go to letsgodiving.com.au.