At this darkest, coldest time of the year, it seems a kind of midwinter madness to take a canoe on to a Highland loch in the deep of night. But we came here for the summer solstice, so it feels right to return. We are the Swallow, set for adventure. The moon is full, but muted by a thick mist. As we cut across the loch, the black water fades without seam into grey cloud, all the familiar landmarks on the shore dissolving. The silence is broken only by the slap of paddles and the creak of boat until unseen geese are startled. Their rising hullabaloo erupts into a storm of wingbeats and splashing till they circle above and settle again, squawks fading. We make for the dark island, feeling like the Dawn Treader on the brink of nightmares, then judder across a skirt of ice that cracks and splinters beneath us. Now we are the Endurance at the ends of the earth. Our vessel stowed on the frosted shore, we head for a clearing at the foot of giant beeches, sweep away leaves and dig out a circle of turf for a fire. Flasks appear, bowls of warm custard on cake, mugs of hot chocolate. We make our beds in bivvy bags and I spend the hours trussing myself in ever more layers of fleece, down and discomfort, my body stiffening into cold. On this longest winter night, the moon has suffused the fog with a strange half-light, and I am as wakeful as when midsummer will not surrender the sky. At last it is morning and time to move. Clearing camp, we discover hair ice pluming from a fallen branch like candy floss, shiny white and soft to touch. An owl makes a wild, demonic shriek from deep in the trees, and we depart the forbidden isle. At first the canoe scrapes across the newly frozen ice ring before breaking through into water the colour of mercury. Beside us, the reed beds are furred with hoar frost, crackling as we brush past. Cloud holds sway all around, hiding horizons, smudging forest and land, blurring edges. Quietly, we slip back to civilisation, fugitives from another world.