Danakil Depression, Ethiopia

Sam has a thing for intensely hostile environments. Phil doesn't. For the first time ever we decided to split up, with Sam joining an extraordinary expedition into the badlands of the Afar. Phil read his book.

The jaunt into the world's most vicious desert required a fully kitted-out Land Rover convoy. Armed guards riding atop the jeep were not necessarily comforting, but the threat from rogue nomads was very real.

In this eerie landscape the ground is of jagged basalt and the fumes from bubbling sulphur bleach clothing. A few people brave the environmental extremes to cut salt and load this valuable resource onto camel trains that cross hundreds of miles to be sold for $5 a slab.

The climax of this geologist's dream field trip is to peek over the edge of a volcano's crater and into a cauldron of magma. Erta Ale is one of only a few flowing lava lakes in the world.