Where is the South American railway stretch popularly known as "El Zig-Zag" found?

Question

Which railway has the highest line in South America and the second highest in the world, second only to the one which connects Qinghai in China and Lhasa in Tibet?

Answer 1

Between Cusco and Machu Picchu, Peru
The zig-zags start as the line climbs steeply out of Cusco, or Qosqu, and continue for five series. Zig-zags and switchbacks are not uncommon in railway lines in the Andes, though not usually so many in the distance.