Seemingly a single, seamless unit, the stair is composed of two elements—treads and mezzanine—and held in place by two distinct strategies: The stairs are welded to, and cantilever out from, a series of steel tubes concealed in the walls; the mezzanine 

is attached on one side to a steel beam, and hung at two other points from rods attached to the roof structure.  190+ Best Modern Staircase Ideas from Harlem Renaissance