Machu Picchu

Constructed around 1450 CE under the Inca emperor Pachacuti and abandoned approximately 100 years later — possibly during the Spanish conquest, though the Spanish never found it — Machu Picchu sits on a narrow ridge between two mountain peaks above the Urubamba Valley. Its 170 structures include temples, palaces, agricultural terraces, and water fountains still fed by the original spring.

The Inca construction technique uses polygonal masonry with no mortar: stones are cut to interlock precisely, with the joints slightly angled to shed water, and the entire structure designed to flex during seismic events. The Intihuatana stone ('Hitching Post of the Sun') is a precisely carved ritual pillar aligned to the movements of the sun at the solstices. Astronomer David Dearborn has identified over a dozen significant celestial alignments in the site's layout. The full astronomical programme of the site remains a subject of active research.