Machu Picchu with the Huayna peak: The ruined city was built by the Incas in the 15th century at an altitude of 2,430 meters in the Andes (Peru).
Built at 2,430 meters with no wheel and no iron tools — every block fitted by hand. Abandoned around 1572, found again in 1911. The jungle kept the secret for the better part of four centuries. © W. Bulach, CC BY-SA 4.0, via Wikimedia Commons

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