Robin Harvie was a fairly ordinary runner. He ran his first marathon after a bet. Then he found that although he couldn’t run fast he could run long distances—very long. A casual hobby turned into a 120-miles-a-week obsession and a training route along the River Thames morphed into a promise to himself that he would tackle the oldest and toughest footrace on earth: the Spartathlon from Athens to Sparta. This race a recreation of Pheidippides’s legendary journey is 150 miles long crosses two mountain ranges and is the toughest race on the ultradistance runner’s calendar. It isn’t at all ordinary.

Harvie’s experience—from the mundanity of daily training routes to the extreme tests of the desert’s scorching heat and the darkest hours of the night—reveals the profoundly intoxicating experience of running and the ways in which every mile taken is both a step further into the unknown and a pace deeper into the self.