This banner is just awful. For a start it is a lot closer to 25km than the stated 16km so doing it by foot is very taxing. Avoid it. If you want to do it do the first 6 missions, they are relatively easy and you get the Krakow letters with a nice background. If you already started the 7th OK, bite the bullet and do 7-12, but never, under any circumstances, start the last 6 missions.
Most of the last 6 missions involves covering 500+ meters between portals with nothing ingress related inbetween. Just lots of empty streets with a portal here and there, and you have to get them all in a sort of zig-zag motion. The last mission is more or less hell. When I started it the stated average time to do it was 2 hours and this is not overstated. It is easily over 5km long, and that is for 8 portals and 1 waypoint. That's it. No other portal in sight. There is nothing else to do than just blindly walk next to a stinky river, once cross the moat to get to a church or something and then back, cross a busy (3 lanes in each direction) highway, sneak through a shopping center parking lot etc.
Oh yes, once you are done you are about a 2.5km walk away from the city center. Just what you need to ponder stopping playing this game.