The Orkneyinga saga refers to Helliar Holm as ‘Hellisey’ or ‘Eller Holm’. The saga tells of Swein Asleiferson hiding his boat in a large cave here when he was being pursued by Earl Harald. The most prominent feature on the island is the 18m tall lighthouse. It was designed by David Alan Stevenson, a cousin of Robert Louis Stevenson, the famous author who wrote novels such as Treasure Island and Dr Jekyll and Mr Hyde. The lighthouse is lit by a solar-powered filament and changes colour when viewed from the sea, depending on the ship’s position. If red or green, the ship is too close to land. If it is white the ship is on a safe route through the String.