Advice for days apart from Lisbon and Porto

Óbidos can be seen in a couple hours and given your time constraints, Nazaré could easily be skipped. When we visited we spent four nights in Tomar and took a couple day trip, three nights in Coimbra, one night in Óbidos and two nights Nazaré. Tomar and Coimbra would be my choices. Evora is nice but visiting it takes you a couple hours further east and you’d need to backtrack to get to back to the other places.

Where you decide to visit should depend on what you want to see in each place. Fortunately, distances between sites aren’t terrible and one can enjoy stops en route to the next lodging location if you choose a rental car option. We had a rental car.

In May 2025 we spent 2 nights in Coimbra en route to Porto from Lisbon driving a rental car. We enjoyed our visit to the university and spent most of our first day visiting the various buildings including the library and Museu da Ciencia. Wonderful 9€ pp lunch (buffet including several choices of hot and cold dishes, veg & meat, dessert, wine & coffee) at the Cafeteria near the Museu da Ciência. We thought that 2 nights was enough to see the main sights and more. We also stopped at Tomar for a few hours to visit the Convent of Christ which was one of the highlights of our trip. Definitely enjoyed people watching at an outdoor table in the shade at Café Paraiso (RS guidebook recommendation).
While in Porto, consider taking a Viator day trip of the Douro valley. We were very happy with our chosen day trip as it included wine tasting at a vineyard, a 45 minute river cruise and a wonderful lunch accompanied by plentiful servings of wine at another vineyard. In our opinion, the extra cost of renting a car was worthwhile for the flexibility it provides in terms of timing and destinations.

Sintra is very easy to get to via public transit from Lisbon. I would not bother adding this to your rental car day but rather do it as a side trip for a day or afternoon while you are in Lisbon.

First, at least in my judgment (and I'll admit I'm a relatively slow traveller), visiting 4-5 cities in four days will inevitably be frenetic, not matter how you travel. Second, if you rent a car, due to heavy traffic in the big cities you may spend a significant part of the first of those four days getting out of Lisbon, and a significant part of the fourth getting into Porto (and then parking).

Otherwise, it's hard to make recommendations among your eight proposed intermediate destinations. For most tourists, I'm sure all of them would be worth-while. The only one of those eight I have visited is Coimbra, and I can recommend it strongly, though I can't say whether it would be better for you than the other seven. However, I believe that most of those destinations, perhaps all, are accessible by train, so the train is what I would recommend.

One other thing: Unlike the seven cities you listed, the Douro Valley -- rather obviously -- is not the kind of place where you park, stroll around the tourist sites, and then depart from in one day. If the Valley turns out to be an important choice for you (and as you like wine and being outdoors, it could be), you might consider going from Lisbon directly to Porto, and then from Porto, up and down the Douro for one or two days. You could then easily fill your additional free days in charming historic towns in the Porto area, like Guimarães and Braga.