Map of Harlech, Porthmadog & Y Bala 1:25,000 scale (4cm to 1 km or 2.5 inches to 1 mile) With this map you will receive a code for use on your iOS or Android smartphone or tablet. Map sheet number OL18 in the OS Explorer series is the perfect map for exploring the area of Harlech, Porthmadog and Y Bala. This dramatic region of the Snowdonia National Park is a walker’s paradise with mountain trails and coastline ready to be discovered.Highlights of the area include: Bala, Llyn Tegid, The Precipice Walk, and Harlech Castle. ISBN - Standard version:  9780319242575 Edition - Standard version:  2015-05 Publication Date 01/05/2015