It was built between 1901 and 1905 to allow workers access between two hydroelectric power plants.
from Travel Feedly http://www.ibtimes.com/el-caminito-del-rey-photos-footpath-spain-reopen-15-years-after-kings-little-pathway-1850244
from Travel Feedly http://www.ibtimes.com/el-caminito-del-rey-photos-footpath-spain-reopen-15-years-after-kings-little-pathway-1850244