The best walk we did in Spain was the Cares Gorge, in the Picos de Europa. Spectacular and enjoyable, the walk took us 3.25 hours each way, which is exactly the length of time indicated on the signposts. We started at the carpark up from Poncebos and walked to Cain and back. The mountains in the Picos de Europa rise to 2,600 metres, so there was still a little snow at the top of some of them. Even though it was May, there were still quite a number of other walkers.
My designated map carrier had forgotten the map (this is disputed), but you can’t go wrong on this walk.
The track is wide enough, though the first time you meet people coming in the opposite direction and you pass them on the outside you tend to stop walking for a second or two.
On the way back, just round the corner from the above photo, some rocks came crashing down onto the path, just missing a couple of walkers in front of us, who were badly shaken.