For Spanish residents, a spare tyre or puncture repair kit must be carried in the vehicle, but if your car is registered outside Spain this is not obligatory
The N-621 down into the Picos area is good, peel off the coast road around Colombres. Then further down off that road, the CA-185 from Potes upto Fuente Dé is excellent. There’s also a Parador at the end of the 185 (it’s a dead-end road effectively), if you’re looking for a nice comfortable place to stop, with a decent carpark and an excellent view
Hi
One thing on my bucket list is to visit Sad Hill cemetery, quite close to Santander actually.
This was a film set created especially for the film The Good, The Bad and The Ugly and was the location for the climatic scene at the end of the film where they fight for the gold in the ‘unknown’ grave
It was partially restored in 2016 with recorded speeches from Clint Eastwood and James Hetfield (lead singer Metallica) who, when playing live, always walk on stage to the 1966 soundtrack of the music where Tuco runs through the graveyard looking for the grave containing the gold
I w old echo Wardy5’s recommendation for Fuente De, you can take a ski lift up the mountain. Not far out of Santander are the famous caves with pre-historic drawings. Amazing but so famous that the names escapes me, you’ll have to Google it.
You’ve probably got accommodation sorted but I recommend the following chains: Paradores in Spain and Pousadas in Portugal. All were comfortable some were very interesting places to stay in.
Re. Driving/car stuff, apart from the obvious stuff eg hi-vis vest(s) I now add a battery starter pack, admittedly I’ve never needed it (oops kiss of death - I’m talking battery here).