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 point. On ships, this position ensured the widest field of view for lookouts to spot approaching hazards, other ships, or land by using the naked eye or optical devices such as telescopes or binoculars. It should not be confused with the top, the platform in the upper part of each lower mast of a square-rigged sailing ship. Source: Wikipedia (en)