Jeju — Munseom

Everything runs out of Seogwipo. Shops on the harbour front load small boats, and the crossing is short enough that you finish kitting up underway. Dives are planned around slack rather than the clock, so a morning may start early or sit waiting for the water to ease. There is rarely a descent line: the group goes in together, gets down fast and regroups on the rock, and the boat follows the bubbles until the last marker comes up. The same coast is still worked by Jeju's haenyeo, the women who free-dive it for shellfish.

The islets off the harbour are eroded volcanic stumps, and they keep that shape underwater: columnar rock faces dropping in steps, ledges and overhangs undercut at the base, and aprons of boulders at the foot. They differ more in exposure than in structure, with sheltered faces gentler and darker with growth while the corners take the full push of the flow. Away from the rock the bottom is coarse sand and rubble, so the interest stays on the vertical.

The coral needs a torch to read properly. At depth the red is gone from the ambient light and the colonies read grey until a beam lands close in, which is when the orange and pink come back. They are thickest on the vertical faces and under the overhangs where the current feeds them, which is exactly where you have least control, so the diving becomes a matter of hand-holds on bare rock and short bursts of finning between them. Small fish stack up on the up-current corners.

This is cold-water diving with tropical-looking growth, and exposure is as much a planning item as the current: hooded and thick through most of the season, with drysuits common at either end as the water heads toward its winter low near 14°C. It rewards repeat visits, since visibility swings hard with rain and swell and a blown-out day tells you nothing about the next one. Divers new to moving water are better served on Jeju's gentler sites away from the islets.