"El Caminito del Rey (English: The King's little pathway) is a walkway, now fallen into disrepair, pinned along the steep walls of a narrow gorge in El Chorro, near Álora in the province of Málaga, Spain. The name is often shortened to Camino del Rey (English: King's pathway)." (Wikipedia)

Apparently the path has fallen into such disrepair that it's virtually un-doable now, but they're planning to rebuild it. Should be completely accessible in a few years (though no longer dangerous/challenging). 

Two unbelievable videos here - one in low-def, and a hi-def walk shot a while later, after the trail had deteriorated even more. Sadly, the person who filmed this, Daniel Ahen, died on 11 May this year at a climbing expedition in the Himalayas.

http://www.youtube.com/watch?feature=player_embedded&v=ZmDhRvvs5Xw

http://www.youtube.com/watch?v=hlw6Yk4WT2I