The iOS app City Maps to Go Pro is free until Sunday. I have used this app to grab a city map for walking around London and Oslo because of it’s offline map feature. That lets me download the map to my iPhone while I’m in the US, and use it in offline mode while in Europe to avoid paying data roaming fees.
I can’t say they are the world’s greatest maps, but they do pretty well, and they are free for the next day or so. If you travel anywhere that would require data roaming fees to access the online map functions of your iPhone, it might be worth checking out.