Jökulsárlón did not exist a century ago. The lagoon began to form around 1934, as the Breiðamerkurjökull glacier tongue — an outlet of Vatnajökull, Europe's largest ice cap by volume — retreated and left a deep basin that filled with meltwater. That basin is now Iceland's deepest lake, plunging about 248 metres, and it keeps growing as the ice front pulls back roughly 200 metres a year. Icebergs the size of buildings break from the glacier and drift across the water, some holding ice more than a thousand years old. They glow in milky blue and turquoise, and darken almost to black where trapped air is densest; the thin dark bands streaking others are volcanic ash, swallowed by the glacier during eruptions long ago and only now surfacing into daylight.
Stand on the shore and the lagoon is never still. Icebergs turn slowly with the tide, and every so often the quiet breaks with a deep crack and rumble as a block splits and rolls over. Harbour seals cruise between the floes all year, hauling out to rest on the ice. Because the lagoon drains to the North Atlantic through a short channel, the current carries stranded ice out to sea, and the waves wash glittering fragments back onto the black volcanic sand beside the outlet — the strip travellers call Diamond Beach. In summer, amphibian and Zodiac boats thread between the icebergs; the rest of the year the shore alone draws you. The scene shifts by the hour and never repeats, which is why it has stood in for Siberia and other frozen worlds in the James Bond films. On clear autumn and winter nights the aurora sometimes appears overhead, and its green bands are reflected in the water between the drifting icebergs.