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 & Wales. However, it is also the largest National Park, with the largest lake in Wales, Bala Lake, plus other peaks & 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, & is available in both standard & weatherproof ' Active' versions. Whatever activities you plan on your visit, you can make the most of it with Ordnance Survey maps.