Map sheet number 239 in the OS Explorer map series is ideal for discovering the Tanat Valley & Llanfyllin in North Wales. The National Trail of Llwybr Cenedlaethol runs right across the area of this map, allowing you to explore the undulating hills of North Wales. Other highlights of the area include: Dyfnant Forest & Lake Vyrnwy. 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 Lake Vyrnwy & Llanfyllin is available in both the standard paper version & weatherproof ' Active' version.