Ulleungdo

Getting there governs everything else. Mainland ferries leave from the east-coast ports, take the best part of a morning and are pulled the moment the sea gets up, so trips are planned with spare days at both ends and the dive schedule stays provisional. An airport has been under construction on the island for several years, but until it opens the crossing is the only way in. Once there, a handful of small operations work out of the harbour towns, and wind direction picks the sites: the coast is steep with no shelf, so crews move to whichever side is in the lee.

The rock is the attraction. Volcanic cliff carries on below the waterline as near-vertical faces with boulder aprons piled at their feet, and the bottom falls away fast enough that depth has to be managed deliberately rather than drifted into. There is no hard coral and very little sand, so colour comes from brown seaweed on the shallow rock and encrusting growth further down, and the interest is structure, shadow and the light coming through the openings. In summer a thermocline sits partway down the profile, and the water under it is a good deal colder than the surface reading suggests.

This is a domestic destination more than an international stop, and it suits divers who already like cold water and rock. Exposure protection should be picked for the bottom of the temperature range rather than the top, and nothing is collected off these shores, since the inshore fisheries are village-managed. December through February is off entirely. In return you get an island most divers never reach, water clearer than the Yellow Sea coasts where most Korean divers train, and a working squid port whose boats light the sea offshore after dark.

Topside fills the days the boats cannot run. A coastal road now rings most of the island, the walkway paths cut into the cliffs are worth the time, and Seonginbong, the high point, is a half-day walk. The Dokdo passenger boat sails from here in settled weather, though landing depends entirely on sea state and is refused often enough that nobody should build a trip around it. Squid, mountain greens and the local beef are what visitors get pushed toward at dinner.