Seilebost beach on Harris in the Western Isles forms a peninsula of about 700 m wide at its root against the rocky knoll of Aird Horgabost in the south. From here it progressively narrows for 1.3 km northwards to a narrow neck of sand. On the west side, Tràigh Seilebost is a straight and gently sloping beach which extends seawards for 300 m and includes wave-built swash bars.
On the east, the extremely gentle slope of the inter-tidal sandflats of Tràigh Luskentyre extends inland. The western coastal edge is backed by a nearly continuous foredune ridge of up to 10 m high, except in the south where the foreshore is backed by an undercut old and stable machair surface. Towards the north of the peninsula, a healthy and prograding foredune ridge with extensive marram Ammophila arenaria cover has developed.