The crux is at the very beginning. The guidebook says a "violent move" and I totally agree. After that, it follows some cracks till a steep slab climbing that looks more difficult than what it actually is. Scary if you don´t like slab climbing (if you don´t like old school slab climbing just don´t go to El Yelmo).
Starts on the right side of the flake called "el gendarme" (well bolted) and goes straight more or less until the summit of el gendarme. To finish, it follows the last pitch of the "Walkiria" route. Get down to the West; there is a very easy route that you can downclimb (5.3), called La Valentina. Do not take off the shoes, though.
Bolted but some gear is needed as well (friends).