Askja Caldera

Askja is a volcanic caldera deep in the barren Icelandic highlands, inside Vatnajökull National Park. Its collapse left Öskjuvatn, a vast, near-black lake and the deepest in the country, and beside it the smaller Víti crater with its milky, faintly warm water. Reaching it is half the appeal: a long day on rough highland tracks across lava deserts and through unbridged rivers, in a landscape so lunar that Apollo astronauts once trained nearby.