‘Fascinating, magisterially researched, and brilliantly written.’ Steve Silberman, author of NeurotribesThirty-two days underground. No heat. No sunlight.4 June 1938. Nathaniel Kleitman and his research student make their way down the seventy-one steps leading to the mouth of Mammoth Cave. They are about to embark on one of the most intrepid and bizarre experiments in medical history, one which will change our understanding of sleep forever.Undisturbed by natural light, they will investigate wha...