Robert Macfarlane said this quote

“ From my heel to my toe is a measured space of 29.7 centimetres or 11.7 inches. This is a unit of progress and it is also a unit of thought. 'I can only meditate when I am walking,' wrote Jean-Jacques Rousseau in the fourth book of his 'Confessions', 'when I stop I cease to think; my mind only works with my legs.' Søren Kierkegaard speculated that the mind might function optimally at the pedestrian pace of three miles per hour, and in a journal entry describes going out for a wander and finding himself 'so overwhelmed with ideas' that he 'could scarcely walk'. Christopher Morley wrote of Wordsworth as 'employ[ing] his legs as an instrument of philosophy' and Wordsworth of his own 'feeling intellect'. Nietzsche was typically absolute on the subject - 'Only those thoughts which come from 'walking' have a value' - and Wallace Stevens typically tentative: 'Perhaps / The truth depends on a walk around the lake.' In all of these accounts, walking is not the action by which one arrives at knowledge; it is itself the means of knowing. ”