Hey Karin, the main Market Square is always a good place to start - it;s the largest one in Europe and features St. Mary's church, St. Adalbert's church (kosciol sw. Wojciecha - one of the oldest in Krakow), the medieval clothhall and the old city hall tower. Not to mention all the beer gardens, bars and restaurants. Wawel castle and cathedral are a must, with several exhibitions to choose from. If you only want to see one - I recommend the Treasury or the Oriental art- as the exhibits might be unique to what you will see in other european countries.
Take Kanonicza street to the Castle - it;s one of the oldest and prettiest streets. Another thing of interest is Kazimierz, the old Jewish Quarter - there are several synagogues and museums worth visiting. Finally, go to Wieliczka Salt Mine - it is on the Unesco list and features entire chambers and chapels carved out of salt. An absolute must see. Drop me a line if you decide to go and i can give you more advise - I lived there for several years.
how are you