I use Spyglass for on-road and off-road navigation. I mark waypoints, save locations to get back to them later. It allows to read maps with only GPS signal and shows your gps coordinates, altitude, speed and more.
But it hasn't got turn-by-turn navigation. https://itunes.apple.com/app/spyglass/id332639548?mt=8&at=11lLc7&ct=fs