@glaskows regarding the Picos de Europa I would get the guidebook by Cicerone Press https://www.cicerone.co.uk/walking-in-the-picos-de-europa. Choose an easy route and take it slow. Enjoy the views, the sights and the sounds. Take it all in and not try to do it too fast. Keep a hike to a sensible distance, maybe 10km and keep the amount of ascent below 300m initially. Of course, these numbers are purely subjective and just my opinion. Do the easy stuff well and enjoy it. Then you can progressively move onto a harder hike.