Portugal in mid March for 8 days

We only did a couple of days in Porto to see the city and do port lodge tours, so we missed out on the Duoro Valley. Kicking myself for skipping that, but I guess there's always next time. I would highly recommend doing the port tour at Graham's. Spring for one of their "Super Premium" tastings, as it is not much more expensive than their regular tour + tasting and the quality increase exponentially. They have a restaurant on site called Vinum that is great for lunch after you get drunk at a mid morning tasting.

A couple of things worth seeing that are in between Porto and Lisbon are the University and Joanina Library in Coimbra and the Templar Castle in Tomar.

Sintra is a place that definitely deserves a couple of days. Quinta de Regaleira, the Moorish Castle, Pena Palace, and Monserrate Palace are all must-see in my opinion. Tivoli Palace is a really cool hotel there.

It's hard to go wrong in Lisbon, but I would mention that Pasteis de Belem is a must visit for pastries and is right down the street from Jeronimos Monastery. It will likely be packed, but the line moves fast. I would also note that the Santa Justa Lift is dumb and a complete waste of time if there is a line. If it's not crowded then it could be convenient. There's a cool archaeological museum where it drops you off up top if you do decide to ride it.

We were in Lisbon for 5 days in November and stayed at Casa Balthazar. You will enjoy Lisbon as there is a lot to see. Easy day trips from Lisbon to Sintra, Cascais or Evora by train. Just be sure of which station to use. The Metro is very easy to use also. We enjoyed a very good meal in Lisbon at Ramiro (seafood restaurant).

I would add Fatima as a stop between Lisbon and Porto. Just takes a couple of hours to check out.