Cnoc Freiceadain (ND012653) consists of two long cairns, set at right angles to each other on top of the Hill of Shebster. Neither cairn has been excavated. For much of their length the mounds are low, but the southern cairn has higher mounds at both ends, and the north cairn has a round mound at the south end. These three mounds provide the name Na Tri Shean (the three fairy mounds) although this name is now applied only to the south cairn. It is probable that three separate round-chambered cairns were incorporated into two later longer structures. Low horns can be seen at both ends of the southern cairn, and at the north end of the northern cairn, defining rectangular forecourts.
The south cairn 'Na Tri Shean' is one of the longest of its type, approximately 70m long. There is probably a chamber under the round mounds at either end. The north cairn 'Cnoc Freiceadain' is nearly as long, but the body of the cairn has been extensively disturbed down the centre.