OS Explorer Maps OL17, OL18 & OL23 Snowdonia National Park in North Wales contains Snowdon, which at 1085 m (3560 ft.) is the tallest mountain in England and Wales. However, it is also the largest National Park, with the largest lake in Wales, Bala Lake, plus other peaks and paths to explore. This map bundle contains all 3 OS Explorer Maps for the National Park with a discount of 20% compared to the cost of buying them individually, and is available in both standard and weatherproof \'Active\' versions. Whatever activities you plan on your visit, you can make the most of it with Ordnance Survey maps.