Machu Picchu, Peru

Machu Picchu, built by the Inca emperor Pachacuti around 1450 at 2,430 metres altitude in the Peruvian Andes, is the finest example of Inca architecture and engineering. Its dry-stone walls fit together so precisely that a credit card cannot be inserted between stones, using no mortar — and the site was built on an earthquake-active zone using a system of terraces specifically designed to drain water and prevent landslides.