Poland is a hidden landscape treasure. Wide rye fields, hills, pine forests, lakes, incredible skies, unique culture. Don't go to the Tatra mountains because you will not find anything better than you already know from the Alps, etc. But you must go places like Roztocze (south-east) or Bieszczady. A trip from Warsaw to the south-east corner can include both Roztocze and Bieszczady.
If you go north then you need to go Mazury. Don't stay in known cliche places, but explore smaller villages. Then drive to the Poland's north-east corner at Suwałki. There are pine forests, rye and wheat fields and lakes everywhere there. A landscape photographer's paradise. If you go to Mazury stay a night or two in Villa Mamry on lake Święcajty (GPS 54.172907, 21.804050). It's a scenic Bed and Breakfast right on the lake. Very inexpensive, but incredible quality, with a wonderful owner. The owner speaks German, so if you do too, then the communication will be easy. It can be your base for exploring the area. You can also rent a boat or a bike from there. A true treasure.