Alexander von Humboldt, whose marble features greet visitors to Berlin's Humboldt University, was the most admired scientist of his day. But the achievements for which he was most celebrated in his own lifetime were never quite perfect. When he climbed the Chimborazo, at the time believed to be the highest mountain in the world, he did not quite reach the top; he established the existence of the Casiquiare canal, between the great water systems of the Orinoco and the Amazon, but this had been well known to local people. Cosmos, the immense work meant to give a synthetic account of the natural world, was left unfinished. This was not accidental. Humboldt's pursuit of an all-encompassing, immersive approach to science was a way of finding limits: of nature and of the scientist's own self. A Longing for Wide and Unknown Things portrays a scientific life lived in the era of German Romanticism -- a time of radical change, in which new ways of living seemed possible. Humboldt's travels in South America were motivated both by scientific curiosity and by other desires that are less easily identified.0As he himself admitted, he 'would have sailed to the remotest South Seas, even if it hadn't fulfilled any scientific purpose whatever'.