A crow's nest is a structure in the upper part of the main mast of a ship or a structure that is used as a lookout. This position ensured the best view for lookouts to spot approaching hazards, other ships, or land. It was the best device for this purpose until the invention of radar.
In the early 19th century, it was simply a barrel or a basket lashed to the tallest mast. Later, it became a specially designed platform with protective railing. The barrel crow's nest was invented in 1807 by the Arctic explorer William Scoresby, Sr. Sometimes, the term is used metaphorically, in reference to topmost structures in buildings, towers, etc. Since the crow's nest is a point far away from the ship's centre of mass, rotational movement of the ship is amplified and could lead to severe seasickness, even in accustomed sailors. Therefore, being sent to the crow's nest was also considered a punishment.