From Lisbon, we took the train to Porto, spent 4 nights and took a walking tour of the city. (We love to explore though walking tours - and Sandeman's free walking tours are an excellent way to explore.) The highlights from Porto - visiting Gaia, experiencing a Port tasting (we booked ours through Sandemans and went to Burmester's at the bottom of the bridge to Gaia from Porto.) Visiting the Si Cathedral , which our hotel Curio by Hilton, was very close by.
Back in Lisbon, we took another train to Sintra, a charming village which is centered around the most beautiful and vibrant castle -Pena National Palace. The trip to get there is very far (and hilly) from the train station, so we recommend taking a bus or taxi to get to the gates - and booking your entrance online for tickets- to avoid the crowd. The Palace and grounds will take a few hours to explore- so take your time.
Finally, in Lisbon, we explored the city. We stayed right next to the elevator (warning, street performers love this site and will sing all day and night.) Visited a local seasonal market and enjoyed the jamon and queso- vino - and beer. We took a ride on a Tuktuk, which we highly recommend for a personal easy view of the city.