Map sheet number 255 in the OS Explorer series covers an area in north Wales to the east of Snowdonia National Park. Highlights of the area include: Offa's Dyke Path National trail, Upper Ceirirog Trail & Llwybr Maelor Way. With this map you will receive a code for use on your i OS or Android smartphone or tablet. Find our more at Mobile Download FAQ. The OS Explorer map for Llangollen & Berwyn is available in both the standard paper version & weatherproof ' Active' version.