I have two friends whom I would call world travelers. They both sent postcards of the ancient Inca ruins in Machu Picchu, Peru in 2001. This photo shows the whole site, including the signature mountain behind it. The other photo shows detail of the site.
Machu Picchu was probably built for an Inca Emperor in the mid-late 1400s. It was abandoned for undetermined reasons, and was not known to the Spanish conquerors of Peru. It was discovered in 1911, and excavations are still ongoing.
The site is 80 km (50 miles) northwest of Cusco. It is at 2430 m (7970 feet) altitude. Seeing Machu Piccu normally involves a three-day excursion, once you are in Peru. I would like to have seen it, but . . . .