on top of the Andes, Peru

A railway on which you are quite likely to experience altitude sickness: 4,783 metres or 15,692 ft above sea level!  The Ferrocarril Central Andino (FCCA; the former Ferrocarril Central del Perú) runs inland from Callao and Lima across the Andes watershed to La Oroya and Huancayo. It is the second highest railway in the world (following opening of the Qingzang railway in Tibet), with the Galera summit tunnel under Mount Meiggs at 4,783 m (15,692 ft) and Galera station at 4,777 metres  (15,673 ft) above sea level (in the pic).  From Huancayo the route is extended by the Ferrocarril Huancayo - Huancavelica. In July 2006 FCCA began work to regauge the Huancavelica line from 3 ft (915 mm) to standard gauge: it was finished in 2010. There was also a proposal for a 21 km tunnel under the Andes.