Altitude: arrive in Cusco slowly, or sleep in the valley first

Cusco sits at 3,400 meters, and flying in from sea level hits most people with headaches and breathlessness for a day or two. Spend the first nights lower in the Sacred Valley (Ollantaytambo, Urubamba, around 2,800 meters) and come up to Cusco afterward, drink a lot of water, skip alcohol the first day, and eat lightly. Coca tea helps mildly; the pharmacies sell altitude medication without fuss. Anyone with heart or lung conditions should ask a doctor before going.