So on your way to Åódź (I guess you will be going via Berlin) I would recomend to see:
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(I am ashamed about that, but for sure it is something peculiar): The bigges Jesus in Europe if not in the World
in Åšwiebodzin. Don’t worry, the people there are quite normal, its just the local priest that has been taken some really good stuff
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if you can plan your trip that way, stop in Mostki in one of the truck stops there (I recomend Las Vegas, the smaller one):
lasvegascenter.pl/en.html
There used to be very nice restaurant there. Also, Niesłysz Lake is within walking distance:
But what is even more interesting, if you could drive few miles, or at least if you carry bicycles with you, I would recomend you to see Międzyrzecz Fortified Region, the second biggest fortification system after the Maginot line, build by Hitler for some purpose and then never defended and given up to soviet without a single bullet being shot:Festungsfront Oder-Warthe-Bogen - Wikipedia
You can visit it with the guide: petla-boryszynska.com/index.html
or go explore for yourself, if you are brave enough and can find one of the access points…
Then Poznań, its a beautiful city:
Old town is a must see in my opinion, if you want, I can ask my friends from there what else can be seen.
In Åódź (which is, imho, an ugly city) its worth to see Piotrkowska street - one of the longest market streets in Europe:
en.wikipedia.org/wiki/Piotrkowska_Street
Some parts of it are ugly, some parts are nice, if you walk the whole lenght (sligthly over 4 km) you can see how much changed in Poland in recent years - it is like time travel.
Åódź is also famous for its industrial architecture, it used to be something like Manchester, the mechanisation of the textile industry started there, if we speak about this part of Europe.
Warsaw: Well, you can see Åazienki park:
lazienki-krolewskie.pl/en,home.html
The palace of culture and science (a gift to Poland from Stalin, but I am afraid you will have more of them in Russia)
And old town with a king castle.
But Warsaw is pin in the arse to drive a truck (bans and everything, ask me if you need) and the most congested city in Europe and there is no baypass, if I was you, I would rather try to avoid it and cross the Vistula river in Wyszogród for example.
As for North-East Poland, its famous for its nature. Augustów Lake District and surrounding areas are one of the wildest in Europe. And when you will be passing Suwałki, it will be worth to make a quick trip to Wigry lake:
And see the monastery on the pennisula:
Around Suwałki there is really beautiful area, its a scenic park of post-glacial scenery (i am not sure if I translated that one correctly).
and one of the last places in EU when you can feel that the time stood still - a small villages with wooden houses that do not even have a tarmac road leading to them: