Altitude psychosis on the mountain I first glimpsed Huayna Potosí, a mountain near La Paz and El Alto, when I sailed across Lake Titicaca, the massive freshwater lake linking Peru and Bolivia.

Bolivia's urban hubs of La Paz and El Alto are feats of human tenacity. But beneath the surface lies a fragile balance between nature and human settlement. At an altitude of more than 3,500 metres ...