Miyako-jima

Nearly all of it is boat diving, and the schedule is set by wind and sun together. Day boats run two or three tanks out of the harbours around Hirara and the bridged islands, and because the cavern mouths face every direction, crews shift to whichever coast is in the lee that morning. The clock matters as much: the beams only land properly when the sun is high, so the marquee dives get slotted mid-morning to early afternoon and reef sites fill the ends of the day.

The terrain is a maze rather than a reef face. Tunnels run clean through the rock, chimneys climb from chamber roofs toward the shallows, and holes and arches link one space to the next, so a dive is often a sequence of enclosures with open blue between them. Most of the named formations sit between 10 and 30 m, shallow enough for long dives, but swell keeps pushing through the narrower passages well after the surface has calmed. Away from the limestone, the outer reefs and the shallow Yabiji complex north of Ikema offer hard-coral gardens and drift diving instead.

Not every dive is overhead, and the mix is what makes a week here work. Guides ration the biggest systems, saving them for flat days and filling the rest with reef, wall and current sites, and the shorter holes serve as a gauge of how a diver handles a ceiling before a longer traverse gets offered. April to June and October are the windows when the exposed coasts open up reliably; winter north winds and the typhoon months close them on and off, so a trip built around the caverns wants spare days in it.

It rewards divers who are steady in the water and enjoy terrain over species lists. Anyone with a wide lens and reasonable trim gets the most from it, and photographers working with natural light have a great deal to play with. Those who dislike overhead environments can still fill a trip on the coral and drift sites, though they would be paying for the island's main draw without using it, and divers who prefer hunting small subjects are better served elsewhere in the archipelago.