rent updated cottages in a 16th century estate/vineyard a nice big hostel GO NORTH! Sorry for the caps there, but I wanted to make sure you noticed my enthusiasim. I had 10 days in Portugal this past spring and would highly recommend my itinerary. I flew into Lisbon and spent 3 nights there, regretfully. I liked Lisbon, don't get me wrong, but if I'd known how amazing the north was going to be, I would have only spent 1 or 2 nights in Lisbon. It's a small city anyway so you can see it pretty quickly. From Lisbon, I rented a car and drove up to Cascias for a bike ride (free bikes) up the coast in the morning and then touring around Sintra in the afternoon. You could stay in Sintra (amazing place) or, to break up the driving some more, head to Leiria, like I did. There was a nice big hostel there and some good restaurants. Anyway, then I drove to Viana de Castelo on the coast. It's a charming little village with the most amazing "manor house" where you can rent updated cottages in a 16th century estate/vineyard for a very affordable price. Using my cottage there as a base, I explored the Portugal/Spanish border, including hikes in the national park, a relaxing day in Ponte de Lima (stunning), the markets in Barcelos, the long gracious beaches, and eventually Porto. My only regret is that I didn't have another day for Porto, but that just means I'll have to go back. Oh, and I flew out of Porto to come home. I found that flying into Lisbon and out of Porto was actually cheaper than just going in and out of the same one. Also, just be advised that this route is only feasible with a rental car. I looked into doing it with public transport but since the north is so rural, it doesn't have much. But it's well worth the extra investment!
No matter what, you'll love Portugal. it's been my favorite of nearly 20 countries so far!