A free app for Android, by Topobyte.de.

With the Kraków Offline Map app, you can easily navigate Kraków and get a feel for the city before visiting. It offers a detailed map that can be downloaded to your mobile device and then used to navigate the city even when you don’t have internet access. You can search for places of interest such as museums, restaurants, cafés, hotels, sights, etc. 

Once you’ve downloaded the app, no internet access is required for browsing the map or searching for places of interest, so it will work even if you don’t have a data plan. Additionally, it works even if you don’t have a Wi-Fi connection, as it uses GPS to show the location of places of interest on the map.