Seen from the deck, Rangiroa amounts to a line of coconut palms resting on the ocean. No peak, no valley: just a ring of coral enclosing a lagoon so vast that the entire island of Tahiti could fit inside it, and whose far shore can never be seen. Ships anchor near the northern passes and bring their passengers ashore by tender, usually on the Avatoru side or at Tiputa Pass, where life in the atoll's two villages is concentrated.

Two blues vying for the horizon

The first impression is all about colour. On the ocean side, a deep blue, almost navy, pounded by the swell; on the inside, a palette of turquoise and jade that shifts with the course of the sun. Between the two lies a strip of land barely a few hundred metres wide, planted with coconut palms and dotted with low houses with painted sheet-metal roofs. You explore it by bike or on foot, greeted by residents who live to the rhythm of the tides and the supply boat's visits.

Tiputa Pass and its dolphins

Twice a day, the ocean and the lagoon exchange their waters through the passes, creating powerful currents that draw exceptional marine life. Tiputa Pass is famous for its resident bottlenose dolphins, which come to play in the eddies and leap in the wake of boats, so much so that they've become the stars of the neighbouring village. From the lookout set up on the edge of the channel, you can sometimes see them with the naked eye, fin after fin. Divers come from all over the world to drift in this current among grey sharks, rays and schools of barracuda.

Fins, mask and snorkel

You don't need to be a certified diver to enjoy the show. Drift snorkelling outings carry swimmers over the underwater gardens, borne along by the current as if on a moving walkway, in water of a clarity few places in the world can match. Day excursions also go to the Blue Lagoon, a natural pool enclosed within the reef about an hour away by boat, where baby blacktip sharks patrol in thirty centimetres of crystal-clear water; lunch is then a picnic in the shade of the coconut palms, toes in the sand.

Pearls and vines

The pearl farms around Avatoru open their platforms to visitors: you can watch oysters being grafted and black pearls with aubergine highlights being harvested. A more unexpected curiosity: the atoll is home to a vineyard planted on coral, its vines growing between lagoon and coconut grove; its whites can be tasted at a few local restaurants. The village churches, charming with their facings of whitewashed coral, are also worth a look along the way, as are the copra dryers that fill the roadside with the scent of coconut: life on the atoll still revolves largely around the coconut palm, fishing and pearl farming, and residents are happy to talk about it with anyone who stops.

The port call in practice

• Tender landing; bring a hat, water and sun protection, as shade is scarce.
• Lagoon excursions leave early: book on board as soon as possible.
• Bikes and scooters can be rented near the Avatoru docks; cash appreciated.

Closing the ring

The tender eventually heads back to the ship, and the dolphins of Tiputa often provide one last escort. Rangiroa isn't visited like a town: the atoll is experienced, through salt, wind and the dazzle of its blues. You leave with the feeling of having floated for a few hours on the roof of an underwater world whose door you've only just begun to open.