landmark

the position of a prominent or well-known object in a particular landscape; "the church steeple provided a convenient landmark"

an event marking a unique or important historical change of course or one on which important developments depend; "the agreement was a watershed in the history of both nations"

a mark showing the boundary of a piece of land

an anatomical structure used as a point of origin in locating other anatomical structures (as in surgery) or as point from which measurements can be taken