To get to the inner limestone cave of Sawa-i-Lau, you must dive under a rocky curtain and swim through an underwater tunnel.
When the tide is high, both are under water and in pitch darkness. At less than high tide, the "curtain" is just a few centimetres out of the water.
It's a dive into the unknown. You need a modicum of courage, as you scrape your head along the rock in the dark beneath the island opposite the village of Nabukeru, in Fiji's Yasawas chain.
Two colleagues turn back. It's too cold, they say. And they're claustrophobic. But it's only by visiting this inner sanctum, says the Fijian villager waiting for us inside, that you actually arrive at the heart of the Yasawas, the islands created by a dramatic fault that runs into the South Pacific on the north-western fringe of Fiji.
Only when you’ve visited this cave, says the villager, can you say that you have been to the Yasawas.
"This is the spirit of the Yasawa (singular)," says the villager, standing waist deep on a submerged rock.
It's not completely black in the cave: there's a vent dropping down on the way in, through the ceiling from the tall, rocky island above. But it's black enough to make the nervous queasy.
You need a torch inside. The water is clear and, while not cold, it's crisp, a degree or two cooler than the 26 degrees in the Pacific Ocean, which feeds the caves subterraneously.
The outer cave is a tall atrium. It's well lit through its southern side, which is open.
The inner sanctum is very different. Most of the 20-metre long space is little more than a low gap between the sea water, at whatever the tide, and the limestone roof.
There is no sign of sea life in here, although the guide inside tells us there are small eels in there, somewhere.
This is our fourth visit to Sawa-i-Lau, but this time there is a big change up here, mirroring changes more broadly affecting the Yasawa, a pristine and geographically remote part of the world.
When we arrive in our runabout after a 45-minute voyage from Tavewa Lagoon to the south, we are greeted by Lucy, dressed brightly in a blue floral uniform, who introduces herself as our hostess.
Lucy herds us on the narrow beach and briefs us on the island and its dangers, such as slippery rocks on the water’s edge, and the low rocky overhang on the stairway down to the caves entrance inside the island. ("Drop your head: Don’t damage the rock," says the sign at the entrance.)
Risk managers have been here, we think. On earlier visits, we had locals in stubbies and singlets take us into the rock, and that was it.
Their party trick was to clamber up the sheer rock faces inside the outer cave and plummet into the water, scattering the visitors bobbing around below them.
Now Lucy inducts us, like on a building site, then ushers us to the cave guides on the concrete stairs leading up to the caves' entrance.
Those guides brief us again on the caves and their dangers, before directing us down the stairs to plunge two metres into the outer cave, where the water is around three metres deep.
The guides inside still plunge from great heights inside, to amuse the visitors, but the environment overall is much more controlled, more tightly managed, less spontaneous than it once was. (A gasp echoes around the walls as a reckless backpacker launches from the cave wall right below a local leaping from five metres above him. They land in the water in the same spot. Both surface.)
And they control access to the inner cave, allowing half a dozen at a time through the submerged tunnel. It's more regimented and, in a litigious age, more professionally managed now.
There are four or five long, open tinnies visiting from the Tavewa lagoon down south, each carrying up to a dozen backpackers.
The journey up to Sawa-i-Lau has been fast and smooth, save for the final reach across a strait to the north of Nacula (Na-thewla), which is bumpy and wet, into a stiff nor'-easter and a heavy chop.
Our helmsman, from Joe’s Water Taxi, takes us directly across the channel into the lee of the northern shore, and along to the caves on the rocky island at the strait’s eastern end.
On the beach, Lucy moves from group to group delivering her welcomes and briefings with her soft, bright Fijian smile.
There are half a dozen women sitting in a line behind rugs spread in front of them offering souvenirs. We feel guilty that we don't buy anything, but we've seen its like before. Most of the souvenirs look as though they've been shipped in from down south.
There are many other signs of progress around the Yasawas, an area known for its myriad budget resorts aiming at the backpacker and budget conscious traveller.
Atop Tavewa island, which forms the western boundary of the lagoon that bears its name, there is a telecommunications mast erected a year earlier by Fiji's new mobile phone operator, Digicel.
The tower sits on the island's peak, up a hill that is at times so steep that the locals have installed ropes to maintain traction on the hillside.
From the peak, there are panoramic views around the central Yasawa. The only sounds are the constant whoosh of the wind, and the beat-beat-beat of the wind fan which, along with solar cells, provides tower power.
Along with a primary tower on nearby Nacula, the Tavewa tower brings strong and reliable mobile phone reception and internet access to the central Yasawa.
We're not pleased with this, but the locals are, not least because it makes communication with the outside world reliable.
Many local families have their kids away at school on islands down south, and resorts have offices in Lautoka, on the mainland.
And there are the employment opportunities. Locals were engaged to build the towers, and Api, who manages Otto and Fanny's with his wife, La, Otto and Fanny's niece, now has a second job in onsite maintenance for the two Digicel towers.
There are 17 resorts around Tavewa Lagoon, ranging from the up-market Turtle Island, a little to the south, to backpacker establishments such as Sunrise Lagoon, Safe Landing, Coral View, and Oarsman’s Lodge.
More budget-conscious than backpacker, Otto and Fanny’s, on the palm-heavy southern tip of Tavewa, is famous for Aunty Fanny's afternoon teas (get ice cream with the cake of the day, alternately chocolate and banana).
Most of these cheaper resorts are not known for their food, other than in a negative sense, but Otto and Fanny’s turns that on its head: food is one of its strengths.
Otto and Fanny's boasts Harry Doughty, Fanny and Otto's son, a chef who has cooked at the resort for over 10 years. Harry's food is sensational, particularly at the prices charged.
"Tonight, we are taking you to India," says La, serving dinner on Tuesday. On Wednesday, it's baked reef fish.
Unlike some of the other resorts, too, Otto and Fanny's does not attempt to lock the visitor in to meal packages: you pay for what you eat.
If you don’t have lunch, for example, you don't pay for it.
In the middle of the market in terms of price, a 1.7km swim across the channel from Otto and Fanny’s, is the stylish Nanuya Island Resort, with a dozen bures and another sensational menu.
There is vigorous competition amongst the Tavewa resorts, some gaining an advantage through a tie up with the provider of transport to the region, Awesome Adventures, which operates the daily Yasawa Flyer, a twin-hulled, high speed ocean-going ferry.
The voyage aboard the Flyer is an experience in itself. The four-and-a-half-hour trip north from Port Denarau snakes through the Mamanucas (Ma-ma-newthas), before crossing to the southern tip of the Yasawas, calling at up to 10 resorts on the way to Tavewa, two-thirds of the way up the chain.
The Flyer drops off and picks up backpackers, mainly, many of them on passes allowing them to visit multiple resorts over a week or so. (When you board the Flyer, head straight to the kiosk to get a roti parcel - curried potato wrapped in fresh naan bread: they run out early. And consider the Captain’s Lounge, which at $F20 one-way or $F30 return offers extra comfort, air-conditioning, and "hospitality".)
The Yasawa is a beautiful, pristine, remote area. The water is clear and safe, the reef bright, varied and colourful, the air is clean, and a full day of swimming, diving, lolling about on the beach reading, village and cave visiting, leaves one ready to be sung to sleep by the lullaby of the sighing palms.
IF YOU GO
Air Pacific, Qantas (in codeshare flights) and Pacific Blue offer daily flights to Nadi. Deals are best found through the airlines’ websites or through portals such as zuji.com, airpacific.com, qantas.com, pacificblue.com.au.
The Yasawa Flyer departs Port Denarau, near Nadi, each morning and returns early evening. You can book your Yasawa Flyer tickets online, along with multi-resort passes and the Captain’s Lounge - www.awesomefiji.com/
You can also book resorts directly online. Otto and Fanny's - www.ottoandfanny.com/ Nanuya Island Resort - www.nanuyafiji.com/ Fiji Visitors Bureau - www.bulafijinow.com/