The brough (small tidal island) of Birsay on Orkney island, Scotland, is connected to the mainland by a narrow causeway that is underwater except at low tide. The brough contains some interesting Viking ruins that are on top of earlier Pictist ruins. Here, three youngsters are attempting to cross before the causeway is fully exposed at low tide. The water is very cold. Needless to say, they turned back. The lighthouse on the brough was built by David Stevenson. The Stevenson family built many Scottish lighthouses. Robert Stevenson, who began lighthouse building, was the grandfather of Robert Louis Stevenson who wrote Treasure Island and Kidnapped.