The Douro Valley, which I would compare to Napa Valley, is Portugal’s region for producing exceptional wines and ports. We tasted a number of wines and ports across roughly 1/2 dozen wineries and was impressed with the quality and diversity. Even more so was the price, where good wines were as little as a few Euros and great wines in the 20 to 50 euros. Needless to say, we drank a lot of wine, as some were less than a bottle of water!
Recommendations: Book accommodations at a Quinta! We stayed at the Quinta de Tedo, a very good winery that also is a boutique hotel and Michelin rated restaurant. Also, I would look at a wine tour! This is an efficient way to taste wines at various vineyards, as many need reservations for tastings. We also took a boat tour up the Douro, and that was a great way to see the landscape and number of vineyards! 3-4 days is plenty of time in this region.
Our last stop in Portugal was Porto. Second largest city in Portugal which had great sights, restaurants, more tastings and the Livraria Lello library. It is said that J.K. Rowling was inspired to write Harry Potter when visiting the bookstore and living in Porto teaching English. A very cool experience and need to buy tickets in advance to visit.
We had an apartment in the Ribeira neighborhood, a great location to everything, but, no parking! So, no need for a car. 3-4 days is plenty of time in Porto.