My first glimpse of Tanna's coastline is from the air, at the tail end of a 40-minute flight south from Port Vila, the capital of Vanuatu. When I peer out my window, I spy a string of rock pools in a reef shelf off the island's western shoreline.
At the airport, I'm bundled into the back of a ute and driven north along a dusty road to the White Grass Ocean Resort. In between visits to traditional villages, a giant banyan tree and to Mount Yasur, the world's most accessible active volcano, the resort will be my base for the next four days.
"The diving on Tanna is as good as anywhere in Vanuatu," insists resort owner John Marsh when I ask him, over a tasty grilled poulet lunch, about the island's aquatic treasures. While Marsh concedes that Espiritu Santo, the archipelago's largest island 520 kilometres further north, boasts one of the best wreck dives in the world (SS President Coolidge), he argues that Tanna's coral reefs and water clarity exceed those found on "Santo".
"I've dived off both and I reckon this is better," he says, confidently. It's a claim I'm willing to test.
To that end, I accompany resort manager Wayne Fitzgerald during an introductory shore dive off the jetty out the front of the resort. "Keep your eyes peeled for turtles," he says, before piloting me through a break in the reef that's only just wide enough for a runabout to squeeze through.
We spend the next hour drifting alongside a drop-off that's 20 metres deep. While the often-sighted green turtles fail to materialise this time, there's still plenty of marine life, including some of the healthiest corals I've seen for some time. And the water clarity is indeed as pristine as Marsh had projected.
"There's hardly any river runoff along this coast, so the water's always nice and clear," Fitzgerald explains, after we're back on land.
My dive fuels a hunger to see more of Tanna's underwater world, with those rock pools I'd seen from the plane continually playing on my mind. So, on a rare, overcast morning, I borrow some reef shoes from the resort's dive shop and walk to Blue Holes 1 and 2.
Snorkelling in these rock pools is like swimming in a giant fishbowl. When the tides recede, reef sharks and turtles are occasionally trapped inside, and I spot a banded sea krait wriggling beneath a shadowy ledge. I duck-dive through passageways and float between chambers, never knowing where they'll lead. Best of all is that I'm the only one here.
One pool worth sharing with others is inside the Blue Cave. Dolphins accompany our boat as we speed north from the resort, passing empty coves and fishermen in outrigger canoes. After 40-minutes, our Ni-Van guide abruptly cuts the motor so we can anchor off a reef, near a limestone headland.
"We are here," he says.
Where, exactly? I can't see anything resembling a cave, until he points towards a gloomy rock overhang just above the waterline.
"You swim through there," he says.
Others need no further encouragement to jump in the water. When I see them again, it's inside a cathedral-sized grotto where sunlight streams in through a hole in the ceiling, illuminating an iridescent lagoon. It's otherworldly – the sort of place a Bond villain might utilise as a secret lair. Except that this secret is one worth telling.
Air Vanuatu operates daily, non-stop flights to Port Vila from Sydney, four non-stop flights a week from Brisbane and three direct services a week from Melbourne, with onward connections to 28 destinations within Vanuatu. See airvanuatu.com
Low season stays at the White Grass Ocean Resort start from around $300 per night on a twin-share basis. Airport transfers and breakfasts are included. See whitegrasstana.com
Mark Daffey was a guest of Air Vanuatu and White Grass Ocean Resort.