This year I am travelling to Poland in October. My plan is to mainly see Krakow but I also have a gig booked in Warsaw for a band called Simple Plan. I will be travelling from UK to Krakow then to Warsaw via train for gig where I have booked a hostel capsule. Will spend early part of next day in Warsaw before heading back to Krakow.
I wish to visit in Krakow:
Jewish Quarter 
Salt Mines
Auschwitz 
Market Square
To name but a few!
Would love to hear any suggestions beyond those and for Warsaw too!