Although contemporary culture prescribes sitting still while thinking, a stroll through the history of literature and philosophy finds ample evidence of a counter-message. Remember Friedrich Nietzsche, from earlier in our journey. “Only thoughts which come from walking have any value,” he maintained. Søren Kierkegaard felt similarly. “I have walked myself into my best thoughts,” remarked the Danish philosopher. Walking is “gymnastics for the mind,” observed the American writer Ralph Waldo Emerson. “I am unable to reflect when I am not walking;

