If I got it right this was a path for workers of the first "Water-Electric Company" in Spain to bring in materials for - then new - electricity production dam construction through a waterfall at around 100 mtrs height (way faster than to descend and cross it at the bottom), AFAIK it dates back to the very first years of the 20th century (Solideo, correct me?).
I seem to recall from news paper articles that around the late ´90s some excursionists who used it (as passing it had become cult) plunged to their deaths, the path then was closed by blowing up its first 10 metres within the rocks (so the vid should be from before this date).
Here a picture (with the path disconnected already) that shows the path from the ground (and JFTR, I think the video has it wrong, it is called "El camin
ito del Rey"):
Rattler
