Once I hit the road, I realized that it was a proper highway, but with a cliff face on one side, and a cliff edge on the other. (And no proper shoulders or anything to walk along). Looks like I'm gonna hitch this one!
Of course, right as I was about to stick out my thumb, a bus pulled up! It was like the Knight Bus from Harry Potter. Anyway, I pointed to where I wanted up go (on my phone) and the driver said "¡Sí!" so I gave him €6.20 and climbed aboard.
A short while later (during which I looked out the window and the width of the road only confirmed my decision to not walk it), we were at the trailhead -- which I learned was very popular with day hikers -- and I hopped out and started hiking. Five steps later, I realized that I'd left my hat back at the bus stop where I had been picked up. Damn. Oh well, I guess I'll suncreen it up!