From the EHOWA website:
El Caminito del Rey (English: The King’s little pathway) is a walkway or via ferrata, now fallen into disrepair, pinned along the steep walls of a narrow gorge in El Chorro, near Álora in the district of Málaga, Spain. The name is often shortened to Camino del Rey. The walkway has now gone many years without maintenance, and is in a highly deteriorated and dangerous state. It is one meter (3 feet and 3 inches) in width, and is over 100 meters (350 feet) above the river. Nearly all of the path has no handrail. Some parts of the concrete walkway have completely collapsed and all that is remaining is the steel beam originally in place to hold it up. One can latch onto a modern steel safety-wire to keep from falling, though it can’t hold much weight. Several people have lost their lives on the walkway in recent years; after four people died in two accidents in 1999 and 2000, the local government closed the entrances. To this day it crossing it has been banned. However policing is extremely minimal and many adventurous tourists still find their way onto the walkway to explore it.
Here’s a video crossing.
There is no way I would attempt that and I like heights.