North Stack North Stack North Stack (Welsh: Ynys Arw, meaning "rugged island") is a small island situated just off Holy Island on the north-west coast of Anglesey. North Stack can also refer to the headland opposite the island. This is the site of a redundant fog warning station, comprising a number of buildings, including the Trinity House Magazine, built in 1861, where shells for the warning cannon were stored. These buildings now house a bird watching observatory, giving a view of South Stack lighthouse across Gogarth Bay, and the studio of artist Philippa Jacobs. The Precambrian quartzite cliffs of this headland, including
Geography of Wales Herefordshire and Gloucestershire lie to the east. Much of the border with England roughly follows the line of the ancient earthwork known as Offa's Dyke. The large island of Anglesey lies off the northwest coast, separated from mainland Wales by the Menai Strait, and there are a number of smaller islands. Most of Wales is mountainous. Snowdonia () in the northwest has the highest mountains, with Snowdon ("Yr Wyddfa") at being the highest peak. To the south of the main range lie the Arenig Group, Cadair Idris and the Berwyn Mountains. In the northeast of Wales, between the Clwyd Valley