When in Krakow, visit Wawel Castle with its museum of armors. It will cost you very little and it's really worth seeing.
As for Tatra mountains - it is my favourite place in my country and I love the town of Zakopane with its specific architecture. Although in the summer you will come across loads of tourists, you will find some quiet places there.
There are various attractions in Poland, but Auschwitz is a must see. A thrilling and horryfying experience, but works like katharsis...
When in Torun, try its specialty old as Torun itself: pierniki. Nicolaus Copernicus (Mikolaj Kopernik) was born there. And view the city panorama from the boulevard by the river Vistula (Wisla).
In the Silesian voivoideship you can find Bledow Desert covering 32 square kilometers, the only natural desert in Europe.
In Warsaw in museum of Culture and Science, an ugly relict of socialism, there is a Motorisation Museum, if you're interested.
Bialowieza Forest has already been mentioned. It is an UNESCO world Heritage Site, one of the last and largest remaining parts of the primeval forest that spread accross the great European Plain ages ago.
Another UNESCO Heritage site in Poland is Old City in Zamosc, Lublin voivoideship.
Biskupin near the city of Bydgoszcz is a life-size reconstructed fortified town from Iron Age. You can see how the houses looked from the inside at that time, there even are some dummies there
Hel peninsula is nothing special - me and my boyfriend went to the end of it once. Traffic on the only road there will drive you mad, it will take you hours to get to the end of the peninsula (moving 10km/h, there will be lots of little shops with tacky beach stuff there and only for a couple of minutes you will be able to see the Baltic sea both on your left and rght. Conclusion? Waste of time.
And about Warsaw - it is a city like any other, it has it's charm, but it is a city like any other if you are only driving through.
If you make up your mind on where to go, I can help you with some further information about my country
What else can I say? Almost 30% of my country is covered with forests and they are public property, not private forests, so you can practically drive in anywhere you like. Wildcamping at a lakeside in the forest? No problem, you will find lots of wild beaches, not always sandy, but quiet. In especially forested areas watch out for boars
In the summer you will come accross people selling fruits of the forest and mushrooms by the road. I recommend you stop at some inns by the roads and try one of the following dishes: bigos, pierogi, golabki, flaki, kotlet mielony, kaszanka... too many to enumerate
Polish cuisine is world-famous!
Most of the young
Polish people speak English, as for those middle-aged, you must use Russian or German (German especially in the west). You shouldn't have any communicational problems in city centres and restaurants, hotels. Owners and staff are used to foreign customers. This is one of the ways my country was hurt by the socialism. English language was considered a part of 'rotten, capitalistic West' and socialists wanted to keep us as far from the western world as possible.
If you need any hints, help (useful Polish phrases, local info, etc.), just send me a PM, I will do my best to help you