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"You're bonkers at your age swimming with tuna in the middle of the ocean. Anyway, where exactly is this place?" mutters our daughter.
We confessed it did seem a bit wild, although for us the mystery was why, as regular visitors to Adelaide, we had not done it sooner.
Port Lincoln had somehow managed to stay under our radar until now. Maybe that's its secret.
Certainly, its slow pace of life was part of what made it so engaging.
No traffic lights, no parking meters or wardens, just unspoiled character and enough buzz without all the glitz of other holiday destinations.
Fringed by the blue waters of Boston Bay on the Eyre Peninsula and wrapped in a cocoon of wildlife, there's a hospitable ring to the name Port Lincoln. It is a place like no other, 650km from Adelaide - remote yet still in touch with the mainland. For the 15,000 residents living here, finding such idyllic surroundings must surely have been the hard part.
Once a sleepy little village, today it's the seafood capital of Australia and home to the country's largest commercial fishing fleet driven by tuna fishing, king prawns, rock lobsters and mussel farms.
Fortunes have been made and lost here - the fortunes, in the shape of the multimillion-dollar mansions of wealthy fishermen, are on display for all to see.
Indeed, Port Lincoln boasts more millionaires per capita than anywhere else in Australia.
An inspection of the tourist brochures highlighted several must-do experiences. Front and centre of the attractions: exploring the booming surf beaches, touring aquaculture industries, a visit to the blue tuna farms and swimming with sea lions.
Day one and the weather had turned bleak, but determined not to let this spoil the action, we headed for the architecturally stunning marina and the heartbeat of Port Lincoln at Lincoln Cove. Before joining our charter, it seemed prudent to take a water-taxi tour to familiarise ourselves with the harbour and the endless canals through expensive real estate.
Marina Boat Cruises operates an electrically powered launch that weaves in and out of the canals with quiet precision. The helmsman's local knowledge proved invaluable, pointing out the owners of the most expensive fishing boats, which mansion was part of which multimillion-dollar divorce settlement and did we realise that an abalone licence can fetch as much as $8 million ($NZ10.7 million)?
In two short hours, we learnt more about the area than we could have absorbed in a week.
Next was Adventure Bay Charters, from where we set out for a blue-fin tuna farm owned and operated by the skipper, Matt Waller - whose family have been farming the big fish for three generations. An enormous circular floating holding pen more like a giant fish-net stocking holds hundreds of gigantic tuna that are impounded for months to be fattened up on pilchards before being sold to the lucrative Japanese market for hundreds of thousands of dollars.
For those not keen to enter the pen, you can still feed the fish with pilchards held with long metal tongs from the viewing platform, or descend into an underwater observatory to view the wetsuit squad swimming among the tuna swarms.
We tugged on our wetsuits, snorkels and fins and entered the water with some trepidation. It felt as if we were gatecrashing this fish frenzy. Tuna need to swim their length every second to stay alive and move swiftly and deftly. We were amazed at their ability to avoid colliding with us.
To them, we must have looked like lumbering tortoises.
Later, we dropped anchor at a private beach where the locals were out in numbers basking in the sun. Welcome to Hopkins Island. No sooner had we jumped over the side than we had to share the water with dozens of sea lions. In an instant, we were completely encircled and captivated by these intelligent and playful mammals somersaulting, backflipping and swirling around us with such amazing grace and speed.
Motoring back to the marina, we reflected on the remarkably pristine state of what is one of the largest protected natural harbours in the world. There was not a piece of plastic or a bit of rubbish in sight.
The next day, we headed west to Coffin Bay, a 45-minute leisurely drive from Port Lincoln, for what was to be another nautical adventure.
Some say there's little to recommend the place beyond its oyster farms and its remoteness.
At this time of the year, it's eerily quiet. There are only 600 people living here permanently, with most of those having some sort of involvement with the oyster farms.
Despite the misty conditions, we board Coffin Bay Explorer, a compact 12m boat, and with 11 of us aboard it's a rush to find the best vantage point without being drenched by the salt spray and persistent rain.
Darian, our tour guide, navigates his way past freakish islands with petrified tree roots, mysterious rock formations where seals and sea lions huddle, and deserted beaches alongside the raw national park.
By mid-afternoon, the clouds began to clear and Darian collected a basket of fresh oysters from his farm for a tasting. There could hardly be a better afternoon than this, 10km from shore on one of the most stunning estuaries in Australia and yet we're moored in less than a metre of clear blue water. It's amazing how a good feed of shellfish can restore spirits.
Rain begins to fall again, and in the distance there is the sound of thunder.
Returning to shore, we're all quiet, reluctant to break the spell of tranquillity. This area is so beautiful and remote and virtually untouched.
Dennis and Rosamund Knill were assisted by Air New Zealand, Blis Travelguard and Southern Cross Travel Insurance.
If you go
Getting there: Air New Zealand flies from Auckland to Adelaide five times a week. Port Lincoln is a 30-minute flight from Adelaide. Contact Air New Zealand Holidays on 0800 747-222 or log on to www.airnewzealand.co.nz.
Getting around: A rental car is the best option
Where to stay: Port Lincoln Hotel offers affordable accommodation
Best eats: Sarins (modern Australian), Marina Hotel (seafood), The Oysterbeds Coffin Bay (seafood)
Background reading: Adelaide and South Australia, by Susannah Farfor, South Australia Horizons Beyond, by Tony Baker
Further information: South Australia Tourist Commission, wwwsouthaustralia.co.nz.