I biked between Lisbon and the Douro valley. My favorite area was the Douro valley all the way down to Porto (a nice city) at the mouth of the Douro. The upper Douro valley is very hilly and is covered with vineyards. However, I have heard very good things abou the Minho region in northernmost Portugal just south of the Spanish border. We ran out of time and didn't make it there. In a week, you could bike in both the Douro valley and the Minho region.