Machu Picchu was an ancient Incan city located in the pre-War country of Peru.
Background
The archaeologist exam at the Pioneer Scout camp has a question that directly references the city. It asks "Hiram Bingham III was an American explorer. He went to South America looking for ruins, and wound up finding them! Which famous ruin did he reveal to the outside world?" Machu Picchu is provided as the correct answer to the question.[1]
Appearances
Machu Picchu is mentioned only in the Fallout 76, introduce in the Wild Appalachia update.