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
beacon for 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 has become uneconomical since
the advent of much cheaper and more sophisticated and effective
electronic navigational systems.