Jökulsárlón is a glacial lagoon on the south coast of Iceland, at the foot of the Vatnajökull ice cap, where icebergs a thousand years old calve off the glacier, drift across the water and wash out to sea, and their broken pieces come back onto the black sand beside the outlet like stranded diamonds. There was no lake here a century ago. The Breiðamerkurjökull glacier reached almost to the sea until the 1930s, and as it melted back it left a lagoon that has grown every year since and is now the deepest lake in Iceland, eating its way inland; the channel that drains it to the sea is the shortest river in the country, about 500 metres, and it too shrinks as the lagoon advances. The bergs are the point. Blue, white and streaked with thin black lines of volcanic ash from eruptions centuries ago, they float in the lagoon for months, turning over as they melt, and in summer amphibian and zodiac boats go out among them, right up to the wall where the glacier calves, with harbour seals hauled out on the floes.
Across the road the outlet runs into the surf, and the beach beside it is Diamond Beach, where the waves leave clear chunks of ice stranded on the black volcanic sand, polished by the sea, each one a different shape, melting in the sun; it is the most photographed stretch of shore in Iceland. Arctic terns nest on the sand in summer, the greatest travellers in the animal kingdom, reaching Jökulsárlón after flying from Antarctica, and diving at anyone who walks too close. At dusk the icebergs turn from white to deep blue with the colour draining from the sky, and once the autumn nights turn dark the aurora ripples over the lagoon and mirrors in the calm water between the ice. The lagoon lies on the ring road, and the road crosses its outlet on a bridge. Jökulsárlón is a lake the glacier left behind as it retreated, and every berg in it is a piece of the retreat.