Believed to be built in 1450, Peru's Machu Picchu is a symbolic remnant of the Incan Empire. The old city sits 2,430 meters above sea level, tucked away within the jungle and hugged by its surrounding mountains. Ironically, the Machu Picchu was built out of stone from earthquake faults, yet every building is earthquake-resistant. Said to be so well fit together that not even a knife could fit in-between, the mortar-free design of the walls enables them to move along the earthquakes without breaking apart. Due to the sudden disappearing of the Incas and the lack of written traces, a whole lot of mysteries unfortunately still remains around this mythical place.