I think within 3 days you can't see much places in addition to Douro River Cruise Portugal.
Fatima is a very small town and not much to see, The houses-museum of the little shepherds, Fatima sanctuary and surrounding monasteries and chapels. If you decide travel some other parts of Portugal, then Lisbon is the best choice. Visit the exciting places of Lisbon and IŽm sure youŽll really love it! It is located in southwestern Portugal and has many attractions. Take a trip through Lisbon on Tram 28 and you can view the entire city and the coast. The Castle of St George, Igreja de Sao Roque, Torre Vasco da Gama, Lisbon’s tallest building, Nation’s Park with plenty of fun activities and much more are available in Lisbon, so take a tour and enjoy your trip!
Visit
Things To Do In Portugalpage to get some more information on getting around Portugal.