Medieval underground museum where you can see the history of Krakow; very interactive and interesting. Get tickets in the Sukiennice (big building in the center of the main square).
So many things and restaurants in this neighborhood. It was the Jewish quarter before the Nazi’s moved them into the ghettos. It is still lovely and has wall murals and is very atmospheric. Good bars (Shot bar bang bang, Nowy Kraftowy) and museums, synagogues to visit, and awesome streetfood!