Bolivia

The Altiplano sits at four thousand metres between two arms of the Andes, and holds the largest salt flat on earth — the dried bed of a lake that evaporated ten thousand years ago. When it floods a few centimetres deep the horizon disappears entirely.

South of it is Potosí, once the richest city in the Spanish empire, built on a mountain of silver that men are still tunnelling into by hand. Two versions of the same high, thin, unforgiving air.