The Penthouse Duplex at 427 East 90th Street Create Over 4,700 SF of Mint-Condition Living + 1,400 SF of Private Outdoor Space A truly rare opportunity to combine two full-floor penthouses into a grand-scale, mint-condition duplex with 4,700 interior square feet and 1,400 square feet of private outdoor space across four terraces. With private elevator access to both floors, open river and skyline views, and complete separation from neighbors, this home offers unmatched privacy, volume, and flexibility - all it takes to connect them is one staircase. Penthouse 9 is a stunning 3-bedroom, 2.5-bath home anchored by a dramatic 50-foot-wide great room with floor-to-ceiling windows and a 720 SF terrace spanning the entire width of the building. The open kitchen is finished with custom cabinetry, Montclair Danby marble, and top-tier appliances. The primary suite features a second private terrace and a luxurious spa bath with radiant heated floors. Penthouse 10, directly above, offers four more bedrooms, two additional terraces, and a second 50-foot-wide entertaining space with open exposures and incredible light - perfect for a formal living room, media lounge, or family retreat. Every inch of both homes is fully finished and in mint condition, with smart home wiring, radiant heat, wide-plank floors, and generous proportions throughout. No renovation needed - just add stairs and move in. Gracie Green is a boutique, full-service condominium offering an attended lobby, fitness center, roof lounge, children's playroom, storage, and bike room. Located near Carl Schurz Park, the East River Esplanade, Asphalt Green, and the Q/4/5/6 trains. A one-of-a-kind opportunity to create a grand, turnkey penthouse with spectacular views, privacy, and two massive entertaining levels - at unbeatable value on the Upper East Side. Taxes based on primary-residence rates.