Most Android devices have Google Maps built in. I was amazed to discover you can download and store maps for a city or even larger region, and use them for turn-by-turn voice navigation when you are offline. (You should store your maps on an external SD card, as the files can quickly eat up your storage.)
Offline navigation is useful if you have poor reception on your mobile - or don't have a data plan at all! Before you head out on the road, toggle to “Wi-fi only” to prevent connecting to online maps and use the maps stored on your phone instead. Your phone will function as it normally does.
* The first time I tested Google Maps offline, it wouldn't let me enter an address that was a house number on a highway number. Maybe there's some secret trick to make it work. So I just found the highway on the map, tapped about where I thought the address was, and proceeded with turn-by-turn voice navigation. Close enough - and what do you want for free?! About 8 years ago, an offline GPS navigation app cost me $80.
Google Maps Blog: https://blog.google/products/maps/get-around-town-little-easier-with-new