Many Manhattan duplexes have tiny circular staircases connecting the two levels because space is at such a premium. But not the Rossoffs’ duplex (click to enlarge):
Here is what the Times has to say about this space:

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[B]eneath a double-height ceiling, a custom-designed staircase (Ms. Selldorf’s innovation) pairs walnut spindles with a sophisticated double banister of polished brass. At its base, a 23-by-12-foot gallery with herringbone oak floors anchors the lower level. Ms. Selldorf chose to rip out quarry-stone tile in the gallery because it clashed with the rest of the period-accurate herringbone floors. Three pairs of French doors connect the gallery to the living room, the formal dining room, and a book-lined library/guest suite that has a full bath and a peek of the Hudson River to the west.
The generously sized living room boasts an antique French marble fireplace and large windows that offer Central Park views (although indirect ones, because they face north towards 71st Street):
The library, which doubles as a guest suite, has a full bath and two exposures, one with views of the Hudson River:

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Is all this space making you drool? Let’s grab a bite to eat in the dining room….