hey Covadonga is already nice to visit and the sanctuary. Oviedo not been in years last few bypass it to other areas I will be in August by Cuenca again ::)
You do well to get a hold of a Guia Repsol ahead or when get there in any library , sometimes the gas station repsol has them.
If not Arriondas has great view of the Cantabrico and Picos de Europa on the other. Aviles is great and from there came the conquistador of St Augustine in Fla oldest city in the USA.He is buried at the Iglesia de San Francisco there.
Cangas de Onis great for cider tastings and cheeses.Pravia was an old capital of Asturias ; Ribadesella has the cuevas de Tito Bustillo, Salas has several historical churches and palace de Doriga, as well as the town of Villaviciosa and not far at Tazones, Carlos I, disembark in 1617.
Nothing on spas never been to one. HOpe it helps your plan.