Organic Maps is a free mapping app for Apple and Android phones and tablets, and Windows and Mac computers. It is designed to continue working on a mobile device even if you lose signal, as it downloads and caches OpenStreetMap maps inside your device itself. Even without a cellphone signal, your phone can still receive GPS location signals from satellites and so you can walk around a woodland comparing your location to the downloaded mapping. You can even mark the locations of features when offline.
