Llanes is lovely. When I went to Porto a few years ago I went from somewhere near Llanes over to Navia on the coast for a few days. Stayed in
https://www.hotelpalaciodelosnavas.com/en/ - some great roads including the AS12 along the Rio Navia gorge. From there I rode across to NE Portugal and to the coast at Viana do Castelo. Stayed a night in the Pousada overlooking the bay
https://maps.app.goo.gl/g9Wa8jC86VwRJnD99 From there I went to Porto for a few days and that was as far south I went.
Last year, I did stay in Llanes at Hotel Montemar. Then headed SW across the national parks to stop in Ponferrada at the Ponferrada Plaza hotel. Lovely town surroounded by great roads in Asturias to the north and Castille y Leon to the south.
I can recommend Ponferrada or Navia as places to stop overnight or better, a few days to explore the area. Asturias in general is fabulous. So many good roads, so little traffic.