Northern Portugal must see destinations?

A small group of us are going to Spain/Portugal for a week in September, last year we rode through some of the Picos then across to the Pyrenees and over to France. Very enjoyable except the French rain.

This year we decided to forget the French bit and sail the ferry both ways Portsmouth to Santander and back. We will probably aim for the Picos followed by Portugal.

Are there any great roads/sites to see in that area. It will be a strictly on road affair.

Thanks in advance.