Yonaguni

Diving here runs off small boats out of the island's fishing ports, and the day is shaped by what the sea allows rather than by a timetable. Crews read the swell each morning and pick a coast; when the wind turns, trips are called off outright rather than moved. Most operators are one- or two-boat outfits taking small groups, and briefings are in Japanese unless you have arranged an English-speaking guide in advance, so it pays to book the shop before you book the flight.

The underwater terrain is rock rather than reef. Ledges step down in slabs and terraces, cut by arches, chimneys and swim-throughs that hold hard shafts of light, with soft coral and sea fans holding on wherever the flow is strongest. Sites differ mainly by exposure: the southern formations can be dived in relative calm when the north side is blown out, while the pinnacles on the open west side sit in fast-moving water and call for a quick negative entry and close buddy contact.

The shark dive is a waiting game. You drop onto a rocky shoulder, tuck in behind structure out of the worst of the flow, and watch the blue while the current streams past; the animals may pass in ones and twos, arrive in numbers, or not show at all. The Monument is the opposite exercise, a slow circuit of terraces and channels where the guide points out the features each side of the origin argument leans on and leaves you to weigh them, and where surge across the shallow steps is often harder work than the depth.

This suits divers who already own their buoyancy and are comfortable being put into moving water a long way from help; the island is small and remote enough that anything serious means an evacuation flight rather than a short drive. The winter months that bring the sharks are also when flights and the Ishigaki ferry are most likely to be cancelled, so build slack into the itinerary and expect to lose a day. Anyone after coral gardens, easy snorkelling or a resort routine will be happier elsewhere.