Four days, 26 miles, 14,000 steps (an American woman once counted), 4,200m altitude, and a journey of jaw-dropping terrain culminating in the 'Lost City' of Machu Picchu: the Inca Trail is one of the most demanding but rewarding experiences of your life. But with high altitudes playing havoc with your digestion, improvised hygiene and a gruelling trek to contend with, this isn't just any old walk in the park. Here are my tips on trekking the Inca Trail in comfort, straight from the horse's mouth…