Landmark

A mark to designate the boundary of land; any mark or fixed object (as a marked tree, a stone, a ditch, or a heap of stones) by which the limits of a farm, a town, or other portion of territory may be known and preserved.

Any conspicuous object on land that serves as a guide; some prominent object, as a hill or steeple.

A structure that has special significance, such as a building with historical associations;

An event or accomplishment of great significance; as, Brown v. Board of Education was a landmark of the civil rights movement. Also used attributively, as a landmark court decision.