Definition of "Landmark" :

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

noun: a mark showing the boundary of a piece of land

noun: an event marking a unique or important historical change of course or one on which important developments depend

noun: the position of a prominent or well-known object in a particular landscape

"The church steeple provided a convenient landmark."