Rarotonga is a worn-down volcano in the South Pacific, the main island of the Cook Islands, and its reef is still welded to its shore. Coral islands run a long sequence: a volcano rises, a reef grows around it, then the volcano sinks and wears away while the coral keeps building. Rarotonga is near the start of it, so the lagoon is a narrow, shallow strip rather than a wide bay. At Muri, on the southeast coast, the water is warm and knee-deep almost the whole way out to four low islets. The sand is bright enough to throw the light back up and turn the lagoon a pale milky blue, and a paddleboard goes wherever you point it. Much of the best snorkelling is a short swim from the beach, over coral heads holding wrasse and striped Picasso triggerfish. The water is shallow enough that you can stand up whenever you want.
One track crosses the interior. It climbs out of Avatiu Valley on a staircase of tangled tree roots, with a fixed rope on the last step, to the foot of Te Rua Manga, the bare volcanic spire everyone calls the Needle. It comes down the far side at Wigmore's Waterfall, where the island's children still launch themselves off the ledge into the cold pool. Behind the coast runs an older road, Te Ara Nui o Toi, laid in basalt and coral slabs through the taro and villages long before the ring road. In one valley in the southeast, landowners have poisoned rats every breeding season since 1989, for the sake of a flycatcher found on no other island. The kākerōri was down to twenty-nine birds then. There are around five hundred now. And because the reef is still on the shore, the sea floor drops away a few strokes beyond it. So the humpbacks that come up from the Antarctic between July and October pass close in, and you watch them from a rock on the coast road: a blow, then the white splash of a breach.