Sarah Marshall travels effortlessly from downtown Auckland to a world beyond Earth.

Gas mask clasped to my face, I stumble through a thick cloud of sulphurous fumes as helicopters circle overhead. It's a snapshot more applicable to an apocalypse than a bunch of tourists on a cruise ship stopover.

This visit to White Island, the 200,000-year-old active volcano in the Bay of Plenty, is my induction to a Silversea Cruise of the wild, largely uninhabited and relatively unknown outlying islands that hang from New Zealand like a necklace of precious South Pacific jewels.

Thanks to the absence of any endemic land predators, several ecologists have described New Zealand as being the best example of how life might function on another planet. The sub-Antarctic islands stand out as especially unlike anywhere else on Earth.

Far further south than White Island, the five Unesco World Heritage sub-Antarctic clusters - Antipodes, Auckland, Bounty, Campbell and The Snares - serve as some of the world's most important wildlife sanctuaries. Yet the quota of 1200 visitor permits each year is rarely filled, an indication of just how tricky it is to actually get here in the first place.

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Silversea is one of the very few cruise lines offering the itinerary, on its adventure-seeking vessel Silver Discoverer, which combines expedition-style travel with the comforts of butler service and Moet & Chandon on tap.

From Auckland we travel south, stopping at places where birds progressively outnumber people. Eradicating invasive species is key to restoring these one-time Gardens of Eden, overrun by rats, sheep and combine harvesters.

One of our first stops, Pitt Island - part of the Chatham archipelago - looks somewhat disappointingly familiar; rolling hills and grazing livestock were a European introduction.

I grow to love the sense of isolation that becomes more acute during our long stretches at sea. Although I could opt to spend days listening to lectures, watching documentaries or burning off decadent gourmet dinners in the ship's high tech gym, I choose to be out on deck.

The cruise sets you amongst unique wildlife, like Antarctic terns. Photo / Supplied
The cruise sets you amongst unique wildlife, like Antarctic terns. Photo / Supplied

While crossing the Chatham Rise, we see sperm whales spouting 5m diagonal blows and fluking. Pelagic birds - ranging from graceful, balletic albatrosses to Wedgewood-blue fairy prions and gnarly-beaked northern giant petrels - hang in our slipstream, then disappear in to the horizon where grey sea and sky become one.

A 15-minute trip through the Bounty Islands, a rare breeding ground for colonies of Salvin's albatrosses and erect-crested penguins, proves to be the highlight of my voyage. As wind batters the granite outcrops, birds hang in the ledges, literally clinging to the precipice of existence.

We explore our next stop, the Antipodes Islands, on a Zodiac tour. Here, waterfalls cascade down columnar rocks, formed like the pipes on a church organ, and trickle over a stratified mille-feuille of volcanic ash.

After so many days at sea, we finally set foot on land at Campbell Island, although we can't just merrily skip ashore. Our boots are scraped and dipped in disinfectant and clothing intimately probed with a vacuum cleaner. Only then are we allowed on shore, where purpose-built boardwalks run through the grassy nesting grounds of 99 per cent of the world's southern royal albatross population.

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Symphonies from some of nature's greatest composers are performed on Ulva Island, much closer to the mainland.

Although not part of the sub-Antarctics, it's still swathed in primeval forest and, in the absence of predators, is an ornithological paradise.

Above us, kaka birds feed on the red flowers of a rata tree while below, a Stewart Island robin hops on the ground, to mimic rain and lure out worms.

Even today, New Zealand's sub-Antarctic environments seem so far from our own reality. The journey to see them all may be long but it's definitely worthwhile.

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Detials: Silversea are offering a 14-day trip from Auckland to Dunedin, via White Island, Napier, Chatham Island, Pitt Island, Bounty Islands, Antipodes Islands, Campbell Island, Enderby and Auckland Islands, The Snares, Dusky Sound, Ulva Island and Stewart Island, on December 20.

The writer travelled courtesy of Silversea.