Side trip to Malbork, or focus on Gdansk museums?

Depends on your interests. Which one interests you more? Are you more interested in history or castles? That will give you an idea where you want to spend your 2 days. I researched Gdansk and nearby ahead of time and am giving myself 6 full days there so I can visit all the history-oriented museums as well as do a few day trips (including Malbork).

I agree Solidarity Museum, WW2 Museum, (and Westerplatte) take up 2 full days to do them justice (depending on one's level of interest in history).

But I get the impression that the WWII Museum and Solidarity Museum each deserve their own day.

It's going to depend on your interests. The WWII museum could easily take 3 -4 hours if you linger beyond the time allotted on the audio guide. Solidarity could be done relatively quickly if your intent is just to visit the site where the downfall of the Soviet Union began, and you're less interested in the machinations of the Solidarity movement itself - they do take a deep dive down into the details. Both museums are excellent in their own way - even the two buildings are impressive. At least they're both in the same part of the town, although still a bit of a hike to Solidarity.

If Malbork is really calling to you, then go for it.

You could do both the WW2 and Solidarity museums in one long day with the briefest of lunch breaks which would leave another day for Malbork. I wouldn't want to sacrifice any of those three so I would want to maximise the whole two days.

I spent 8 hours in the Solidarity Museum and 20 hours in the WWII Museum. Didn't make it to Malbork (not a fan of castles). You probably don't need to pre-book any of those activities. You could attack first whichever of the museums you suspect you might want to spend more time in, and see how it goes.

The good thing about your dilemma is that you don't need to commit to either plan. Reservations aren't necessary for any of these sites so you can decide as you travel.

All great feedback. A follow up question for those who have visited the shipyard & European Solidarity Center: how long would you allot just to visit the shipyard/Solidarity Square/monuments? Thinking that in one packed day we might be able to manage both the WWII Museum and the Solidarity sites if we did a lighter touch on the Center/museum itself.

how long would you allot just to visit the shipyard/Solidarity Square/monuments?

The square and monuments don't really take up much time, I viewed them as I walked to the museum and probably spent just a few minutes so it's not an "either/or" decision.

When I was there in April of 2024 there was a fair amount of construction on the grounds around the museum so it was unclear whether there was a clear path to the shipyards - it may be better now. But there is an observation deck up on the roof which offers a good view of the shipyards, and admission to the deck is free.

I feel your pain! The thing you need to also think about is that besides those two museums, Gdansk is (IMHO) one of the best cities in Euroope to wander around and enjoy.

If I were in the same position, I would not skip Malbork. I would probably skip one of the museums. But I'm not particularly into history museums. (I did, however, enjoy visiting the Solidarity Museum. I didn't visit the WWII Museum.)

Having spent 7+ hours at the Solidarity museum today, all I can say is that I was so happy it was the only thing that I scheduled for the day. Fantastic museum, lots of video and audio, lots of exhibits mostly in English along with Polish, and a very helpful audioguide included in the price of the ticket. We don’t see the WW2 museum until Thursday, but I’ve scheduled a full day there too. Hope we don’t need more than one!

Wwe did Malbork with an audio tour. Was interesting, until after 3 hrs we stumbled out into the sunlight and the audio tour said now was time for a break until the start of the second half.
At that point we abandoned.

I had 3 nights in Gdansk. The first day/afternoon, we wandered around the town, getting our bearings. We went to Malbork the next day but got back to Gdansk for dinner and more strolling through town. I really liked Malbork, but I really enjoy castles as well. The last day, I followed Rick Steves' walk through town, went to the Solidarity sights and monuments but did not go through the museum, instead opting to go to the WWII museum which I really enjoyed. It was a lot of walking that last day so my feet were feeling it, but I think what I saw aligned best with my interests so you probably can't go wrong with anything you choose. I also went in December so the Christmas Market was a big draw during the evening hours.