Stroma Lighthouse

sits at the Northern-most point of the island of Stroma and watches over the Swilkie. The Swilkie is the most dangerous whirlpool in the Pentland Firth, occasioned by the meeting of four or five contrary tides.
According to legend, the Swilkie is the place where the salt which maintains the saltiness of the oceans is ground in a giant quern, stolen from King Frodi by a sea-king named Mysing. When Mysing's longship sank off Stroma under the weight of it, he still continued to grind away with it 15 fathoms down and to this day the sea can still be heard roaring through it.