Ordesa National Park, Spain.
Eroded ledges, some walkable, are called ‘Fajas’.
… For those with a head for heights the Faja de Flores is a must. A steep climb leads to the entrance of the Faja nearly a kilometre above the valley floor. At first there looks no place for a path but as you get closer the eroded band shows itself and you can see it winding it’s way along the cliff face. The views change around every corner as you get views of the Sierra de Guara, the southern cliffs of the valley and then the Breche de Roland and the highest peaks in the park. …
That’s a U.K. based company offering this adventure as part of their Peaks and Passes guided walking holiday.
besthike.com 
We were up here in 2008, but did a slightly more pedestrian route which isn’t quite so drastic (though I still got a little vertigo all the same). The link I’ve included below goes to my Flickr set which further links to my GPS route.
http://www.flickr.com/photos/yorkie/sets/72157622514371504
Back in the nearby town of Torla that we were staying here, I saw photos of this route (or a similar nearby route) which in sections were sheer drops, with dowels (metal bars) in the side of the cliff face for hand and foot-holds. Yikes!
It’s a superb route but definitely not for those with vertigo. There are two sections of ‘clavijas’ – iron pitons driven into the rock. The pitons on the way up in the Circo de Carriata are not bad – just 6m up a rocky chimney. The Clavijas de Cotatuero on the way down are a different matter – 30m traverse across a vertical cliff face with only the pitons for your feet. Not for the faint hearted!
The Ordesa National Park is packed with great routes as well as fantastic flora and fauna. Here’s a video from a 3 day hike in the park: http://www.youtube.com/watch?v=iDnkhKtEUhI
Phil