Apr 18, 2006· How serious is a 40 mile walk? April 18, 2006 2:06 PM Subscribe. My friends and I are considering participating in the Keswick to Barrow 40 mile scenic walk (for charity). We are in varying states of fitness. Are we insane? We are all around 19 years old. Some people smoke a lot and get no exercise, some (like me) are nonsmokers and walk for ...