Erta Ale is a six hundred metre-high shield volcano in Ethiopia's Danakil Depression, part of the great African Rift Valley which stretches from Syria to Mozambique, where the Horn of Africa is drifting away from the rest of Africa, and the Arabian Peninsula drifting further north. It is, in effect, a mid-oceanic ridge on land - much of the surrounding area lies almost a hundred metres below sea level. It has two craters, the southern one of which contains one of the world's only permanent lava lakes and erupted with lava flows most recently in 2010.
Getting there is a bit of a challenge - the base camp is four days' journey by road out from Addis Ababa, sometimes over trackless deserts and around a maze of ancient lava flows. There, you begin a 12km hike to the rim of the caldera before setting up camp, hiring camels to carry your gear. Additionally, the volcano is only a few kilometres from Dallol - one of the lowest points on Earth, where three diverging crustal plates meet, and possibly the hottest place on Earth, based on average year-round temperature.
But it's a photographer's paradise: