• Bright Angel & North Kaibab Trails: Arizona, USA

Walk length: 34km; 2–3 days

The Grand Canyon cuts an almighty dash through the Colorado Plateau, is 446km long, up to 29km wide, more than 1.6km deep and just shy of two billion years old. That’s the age of the venerable Vishnu schist at the base of this geological layer cake, which is best viewed by walking from canyon top to bottom and back up again. Follow in the footsteps of the Ancestral Puebloans, using the Bright Angel Trail to descend from South Rim to the Colorado River, via ancient pictographs and a riot of ever-changing rock. Spend a night in the canyon’s bowels before ascending the North Kaibab Trail to read the rock strata in reverse.