Originally, a landmark literally meant a geographic Feature, used by explorers and others to find their way back through an area on a return trip. In modern usage, it is anything that is easily recognisable, such as a Monument, Building, or other Structure. In American English it is the main term used to designate places that might be of interest to tourists - the closest equivalent to visitor attraction'' in British English. In British English the term is less used and only refers to things that are truly visible due to their height or size.
These are often used for casual Navigation, such as giving directions. Examples of landmarks include the Taj Mahal in Agra, Eiffel Tower in Paris, Big Ben in London, Mount Fuji in Japan, Stone Mountain near Atlanta and the CN Tower in Toronto.
A variant is a Sea mark, usually built intentionally to aid sailors on featureless coasts. An example is the tower at Walton-on-the-Naze.