landmark

(noun) the position of a prominent or well-known object in a particular landscape. Example: "The church steeple provided a convenient landmark."

(noun) an event marking a unique or important historical change of course or one on which important developments depend. Synonyms: turning point, watershed. Example: "The agreement was a watershed in the history of both nations."

(noun) a mark showing the boundary of a piece of land.

(noun) 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.