4 October 2023 — Circuit 2.

Built around 1450 under Pachacuti and abandoned roughly a century later, never found by the Spanish and so never destroyed. It sits on a ridge at 2,430 metres between Machu Picchu and Huayna Picchu, on ground engineered as much below the surface as above it — the terraces are layered rock, gravel and soil, a drainage system that keeps a stone city standing on a steep slope in a cloud forest that takes two metres of rain a year. Access is now by fixed one-way circuits; these are from Circuit 2, the classic upper approach.