2 nights in Porto, 3 nights in Lisbon - what not to miss?

I am following this! Good question!

Which month of the year will shape the answer as weather varies.

Also arrival from elsewhere in Europe vs stateside will impact first day.

Open jaw vs return to starting point will make a diference.

2 nights could translate into just 1 sightseeing day or even 3 depending on arrival/departure time.

Forum members can provide more useful and relevant advice with little bit more specificity

I'm looking forward to getting some basic info on what people think are definite must-see's. Specific itinerary isn't needed to answer this basic question.

We enjoyed just walking around Porto, visiting the church of Souls, cathedral, San Bento train station, looking at the blue tiles on some churches, going by the town hall to see the Porto sign, walking along the river and doing a couple wine tastings, and walking across the Luís I Bridge. I wouldn’t classify any of them as must see.

Porto
RS upper and lower walk with detour to cathedral

Depending on time of the year and whether you have 1 day or 2 days or 3 days, trip to Douro Valley or not.

One of the port facilities in Gaia.
1 hour boat ride

Buy RS book (or pick one up from library - even one from 2019 or 2021 will get good enough info), invest couple of hours reading it and then post any specific queries.

For Lisbon:
Plenty of threads on this forum to get some idea's without any specifics in mind

Here's a good place to start:
https://www.ricksteves.com/europe/portugal

Gulbenkian Museum! We were provided with a marvelous 1 1/2-hour guided tour on our RS tour. Wish we had spent more time. The cafeteria in the bottom of the museum is excellent but can be busy.

For Porto, I liked Jardim do Morro at sunset. Also wandering around looking at the street art.

Nice to hear the museum in Lisbon is good because it's really the only thing I know that I really want to see, at this point. I am hoping that others contribute some more for Lisbon.

For Lisbon, riding Tram 28 from end to end. Get on by Prazeres Cemetery (which is worth seeing too) and ride it to Martim Moniz. Make sure you get a seat, and enjoy. Great way to get an overview. Then can take another form of transportation or walk back to the areas that caught your eye.

I like Belém including Jerónimos Monastery, Coach Musuem, Tower of Belém (looking at the outside) and just walking along the Tagus River.

And I enjoyed the Timeout Market.

São Jorge Castle, arriving prior to sunset, and then watching the sun go down (beautiful views and color). The peacocks. Wandering around after the sun sets when they light up some sections, but still dark in other areas. Adds a bit of mystery and feels like you have gone back in time.

I just got back from 2 weeks in Portugal including Lisbon, Coimbra and Porto. Others mentioned a lot of good experiences. The Gulbenkian Museum was excellent but not very big (which for me was perfect). I enjoyed the Monument to the Discoveries with the elevator to the observation deck, Belem Tower and the Pasteis de Belem (even with the line). The best museum for me was the Maritime Museum, next to the Jeronimos Monastery. Especially related to the era between 1400 and 1800, when Portuguese influence was at it's peak.

In Porto, the Sao Cathedral and especially the Sao Francisco church interior (rivals the interior of the Toledo Cathedral) are must sees. The Arabian room of the Stock Exchange Palace is amazing.

In Porto I always go by the Mercado Bilhao, preferably in the morning. And I like the sunsets off the beach at Matosinhos, especially how it exaggerates the yellow color of the Fort of Cheese.