A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses and to serve as a navigational aid for maritime pilots at sea or on inland waterways.
Lighthouses mark dangerous coastlines, hazardous shoals, reefs, rocks and safe entries to harbors; they also assist in aerial navigation. Once widely used, the number of operational lighthouses has declined due to the expense of maintenance and use of electronic navigational systems.