The Barrathon was initially a single event to mark the millennium, and a chance to raise some money for charity at the same time.
From mile 4, the course climbs gradually as the route starts to head east, peaking at around 170 ft just past the 5.5-mile stage.
The next 1.5 miles see the route drop back to sea level as the 7-mile mark is approached.
The route offers some respite with a mile long descent followed by a short but sharp climb of approximately 40 ft before a fairly steady run to the finish point in Castlebay.
The course was officially measured in 2008 by a company on behalf of Scottish Athletics and meets the minimum distance for a half marathon.