View of the ancient houses of Machu Picchu houses, Urubamba Province, Cusco Region, today Peru. The 15th-century Inca citadel, abandoned one century later, is situated in the Sacred Valley on a mounta
The ancient stone houses of the 15th-century Inca citadel, situated in the Sacred Valley. © Diego Delso, CC BY-SA 4.0, via Wikimedia Commons

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