I’ve been to Krakow twice and it’s probably my favorite place on earth!
-If you haven’t booked a place, stay in Kazimierz. It is the old Jewish Quarter and has beautiful architecture, is very walkable - including to the main square/old city - and has great food. Plac Nowy is the square in that neighborhood and has great street food (have a zapiekanka from the rotunda in the middle of the square, and some sausage or a kebab from the stands on the edges) and a different market every morning. (Friday AM from 6 to 8 there is a pigeon market!)
-I have basically never had a bad meal in Krakow and the dollar is so strong that you can really eat like a king if you like. Favorites include: Kuchnia u Doroty for classic Polish food, Nolio for amazing Italian (I have been known to eat here twice in a week), Zenit for really any meal, Ranny Ptaszek for brunch.
-Alchemia in Plac Nowy is my favorite bar in Krakow. Everyone smokes inside, though. Propaganda is also pretty funny, lots of socialist memorabilia.
-If you can see something there or just poke your head into the opera house (Teatr im Juliusza Slowackiego), do so. It’s astoundingly beautiful. The Krakow orchestra is world-class if they happen to be performing while you’re in town.
-Salt mine is very cool. An entire city underground.
-For a hiking day trip, journey to Morskie Oko in the Tatras. Known as one of the most beautiful lakes on earth, tucked up in the mountains. It’s about a 9km hike but no problem if you’re fit. Go EARLY - we ended up hiking down in the dark, which would have been scary if there weren’t like, six German families doing the same thing. If you’re wiped, you can hike up and then ride back down in a horse-drawn carriage!
-One of Poland’s best national parks, Ojcow, is right outside Krakow. Never been but it’s supposed to be beautiful.
Have a great time!