Arka Unskel is 2½ miles ESE of Arisaig at NM693839 and has also been known as Ard Ghaunsgoik and Ard Ghamhgail. Described as on a promontory on the north side of Loch nan Uamh with a heavily vitrified wall. - Richard Feachem's "A guide to Ancient Scotland"
At the point where Loch na Nuagh begins to narrow, where the opposite shore is about one-and-a-half to two miles distant, is a small promontory connected with the mainland by a narrow strip of sand and grass, which evidently at one time was submerged by the rising tide. On the flat summit of this promontory are the ruins of a vitrified fort, the proper name for which is Arka-Unskel.
The rocks on which this fort are placed are metamorphic gneiss, covered with grass and ferns, and rise on three sides almost perpendicular for about 110 feet from the sea level. The smooth surface on the top is divided by a slight depression into two portions. On the largest, with precipitous sides to the sea, the chief portion of the fort is situated, and occupies the whole of the flat surface. It is of somewhat oval form. The circumference is about 200 feet, and the vitrified walls can be traced in its entire length. We dug under the vitrified mass, and there found what was extremely interesting, as throwing some light on the manner in which the fire was applied for the purpose of vitrification. The internal part of the upper or vitrified wall for about a foot or a foot-and-a-half was untouched by the fire, except that some of the flat stones were slightly agglutinated together, and that the stones, all feldspatic sandstone, were placed in layers one upon another.
It was evident, therefore, that a rude foundation of boulder stones was first formed upon the original rock, and then a thick layer of loose, mostly flat stones of feldspatic sandstone, and of a different kind from those found in the immediate neighborhood, were placed on this foundation, and then vitrified by heat applied externally
Additionally the location is said to be the landing spot of Bonny Prince Charlie prior to the ill fated battle with the British.