Rare Opportunity in a Prime Park Block Co-op Create your dream home in this classic six at 21 East 90th Street. Just off Central Park, this spacious prewar apartment offers exceptional layout, charm, and potential in one of Carnegie Hill's most desirable full-service buildings. Residents enjoy a full-time staff, beautifully renovated lobby, a small fitness room, and an unbeatable location.    From your semi-private landing-shared with only one other apartment-you step into a gracious foyer with coat closet and gallery. The spacious living room, serene and quiet, overlooks a leafy courtyard. A large formal dining room connects to a butler's pantry and a thoughtfully designed, state-of-the-art kitchen, complete with extensive storage, Bosch, Miele, and Sub-Zero appliances. Beyond, you'll find the versatile third bedroom and the true upper east side amenity, the service entrance, where mail, deliveries, and refuse are conveniently managed.    The two primary bedrooms are generously sized, each capable of accommodating a king-sized bed, seating area, and additional furniture. One bedroom boasts an en-suite bath and corner location, enhancing privacy and comfort. Both original bathrooms are windowed but will need renovation.  While window air conditioners are currently in place in the bedrooms, there are existing through-wall units in the living and dining rooms.   This pet-friendly co-op welcomes pied-à-terre ownership and allows 50% financing. You'll be well attended to with a full-time doorman, live-in superintendent, small gym, deeded storage, bike room, and complimentary laundry. The coop board requires the new owner install all new windows within the first year of purchase.     The prime location of 21 East 90th Street offers unparalleled access to the cultural and educational riches of Carnegie Hill. Discover the charm of local boutiques, delightful eateries, and the famed Museum Mile. Families will appreciate proximity to esteemed private and public schools. Just half a block from Central Park and the Jacqueline Kennedy Onassis Reservoir, outdoor enthusiasts will find endless opportunities for recreation and relaxation.