An Dunan is a small natural island located at the north end of Tràigh nan Srùban, an inlet that runs north from Camas Uig. This island is located in tidal saltings close to the east shore of the inlet and has structures of unknown date or form located upon it. The islet consists of a raised bedrock knoll in the midst of what is now a salt marsh. Prior to excavation several large stones of Lewisian Gneiss could be seen protruding through the turf on the summit of the knoll which seemed to delimit a possible small curvilinear building. A visible causeway, again composed of large Gneiss blocks, crosses the marsh from north-east to south-west and seems to dog-leg midway. It emerges from a natural promontory jutting into the marsh at the base of a steep rise to the north east and is enveloped by salt marsh before reaching the knoll. The marsh is cut by several natural watercourses, some modern drainage ditches and has faint traces of agricultural rigging running into it around its northern limits and possibly to the east of the site. Much of the landscape around the site has been intensively cultivated and incorporates some of the best preserved agricultural rigging on Lewis associated with the pre-clearance village of Bereiro.