A most unique and sophisticated unit in a lovely PreWar Co-op steps from Central Park and Museum Mile.   This beautiful and gracious duplex apartment boasts a large and graceful living room, over 9ft high beamed ceilings, pleasant city views and great light which streams in from large north facing windows.   In addition to the living room, there is a windowed and charming kitchen with a large pantry, a dining room graced with southern light and a full windowed bath on the lower floor of the duplex.   Up a gorgeous winding staircase with custom-designed wrought iron railings, is a spacious landing lined with bookcases, two  bright bedrooms with great north-facing windows, a den, a full windowed master bath, a half bath and a washer/dryer.   The apartment boasts an abundance of closet space.   There are only three apartments on the floor.   All this in a Full Service Co-op in the most prime location in Carnegie Hill, steps to Central Park and museums, top restaurants and boutiques, as well as shopping and public transportation. Flip Tax: 2%.