As we mounted the crater wall we found ourselves in a different world. Standing on the crater rim I looked down to see a small steaming hole in the ground. I crouched down to feel the heat – it was like a boiling pot. We could have popped an egg in the hole and three minutes later enjoyed a tasty snack.

The crater floor was almost completely level apart from the sharp hornitos that protruded here and there, smoke or steam streaming from their tops. I assumed we would stop here at the rim, but other groups had already proceeded to walk across the crater floor, which was white almost like snow, and crunchy under foot like the lake bed of Natron far below us.