In the notes field of the booking form, she wrote only one line: this is my seventh continent — please let the day we land go slowly.

She is sixty-eight, a retired geography teacher. The first six continents took her twenty-six years: her first trip abroad came at forty-two, marking her pupils’ exercise books on the plane. The last on her list she had saved for the farthest — Antarctica.

On landing day, the Zodiac drew up to the shingle beach and, as ever, the expedition team put out a hand to help each guest ashore. When her turn came, the crew member added a line — we had had a quiet word beforehand — “Welcome to your seventh continent.” On the step that brought her onto land she visibly paused, as though turning one step into two: the first half a journey, the second a completion.

She did not take a photograph; she crouched down first and gathered a pinch of snow into a small glass jar. For thirty years, she said, she had taught “the seven continents and four oceans”, had drawn Antarctica on the blackboard hundreds of times, and today she would carry a little of the real thing home for her former pupils still at the lectern to pass around: let the children touch it, and feel that the last page of the textbook is cold.

At the farewell dinner on the return voyage, the expedition leader, as is the custom, asked those who had “completed their seventh continent” to stand. Three rose that night, and the applause of the whole ship was long. She wrote to us afterwards: when the applause began, what I thought of was not the scenery of six continents, but every night across those twenty-six years of “wait a little longer; put the children through school first”. It was all worth it.

Some journeys are holidays; some are the keeping of a vow. We can tell them apart, and we can hold them.