Hadrian's Wall, Haltwhistle & Hexham (Sheet map, folded)N/A Ordnance SurveyOrdnance SurveyOS Explorer is the Ordnance Survey's most detailed map and is recommended for anyone enjoying outdoor activities such as walking, horse riding and off-road cycling. The series provides complete GB coverage and can now be used in all weathers thanks to OS Explorer - Active, a tough, versatile version of OS Explorer. The OS Explorer Active range of OL maps now includes a digital version of the paper map, accessed through the OS smartphone app, OS Maps.