Just off the square and next to the place you buy tickets to the salt mine is a Thai restaurant in Krakow. Of course we went in for lunch. The food was good and the heat was adjusted per person. We left stuffed.
Underneath Wawel Castle is a cave. Okay, there are many caves. One, though, you can transit through. It's called the Dragon's Den (because of the dragon who used to live there) and is a pretty easy walk as long as you have no fear of the stairs at the beginning.