I want to recommend Organic Maps for offline use while traveling.
We are currently in Italy for a few weeks. I do not buy a data plan. We rely solely on WiFi if needed. We run into difficulty at times but nothing worth paying for. We're also not heavy data users in the first place (with five of us on our plan we never go over 10gb a month and I travel for a living.)
But I've fallen in love with Organic Maps on this trip. It has been our most valuable app. Very user friendly and it relies on openstreetmap data. You download your maps ahead of time. Then a little research...
I simply bookmark where our lodging is, and I bookmark a handful of highly recommend restaurants in the area in which we are traveling, some cheap, some pricier, so no matter where we are, a quick glance shows the nearest restaurant that I've already researched ahead of time.
Bonus as it automatically downloads information from Wikipedia on important locations. So if you're in a church in Siena that isn't covered in the RS guide, often there is info right on the app.
It also shows subway stops and walking trails if you enable that layer. It also shows an icon as to the best places for photos! A quick tap shows you the nearest toilet, water, taxi stand, ATM, pharmacy, police station etc. All offline.
I have no relation to the creators. But this has been the absolute most useful app I've ever used for traveling. My lone complaint is that when calculating the time to walk somewhere, I have no idea where it gets the data as I can't walk that fast! It's been getting more accurate so maybe it adapts? Otherwise, wonderful!