Unique opportunity to combine 52 East 81st Street and 54 East 81st Street and create a 40-foot wide mansion in one of the most desirable residential neighborhoods on the Upper Eastside. A combination, which would offer approximately 14,151 square feet of living space, presents a range of possibilities. Convert and completely redesign as a magnificent single-family home, or enjoy a magnificent owner's residence while maintaining several residential units for lease or personal use. With additional FAR and the absence of a landmark designation, the potential to upgrade or redevelop is practically limitless.Wonderfully located on the south side of picturesque and tree-lined 81st Street, the buildings sit mid-block between Madison and Park Avenues. Central Park and the Metropolitan Museum of Art are around the corner, putting these properties squarely amidst the best culture, recreation, dining, and retail offered anywhere in Manhattan.About 52 East 81st Street:52 East 81st Street is a grand 20-foot wide, 5-story townhome with stunning proportions and exquisite architectural detail throughout its gracious approximately 5,776 square feet of living space. It features a deep, lushly planted south garden and serene terrace. Currently configured as three units (two duplex apartments and one floor-through), 52 East 81st Street may be delivered vacant, affording the rare opportunity for a discerning buyer to create a custom single-family dream home in an unrivaled Upper East Side location, or benefit from the income of a multi-family property. About 54 East 81st Street:54 East 81st Street is a grand single-family limestone mansion, beautifully reconstructed to the highest standard, throughout its approximately 8,375 square feet of magnificent interior space and approximate 2,040 square feet in the delightful South garden, balcony, and fully-finished roof deck with a hot tub. Intelligently designed, this exceptional home features a high-speed Federal elevator, radiant floor heating throughout, a snowmelt system in both the front and rear gardens, dumbwaiter with dual openings, a noise-cancellation and vibration dampening system between each floor, and a central vacuum system. An integrated smart-home AMX system controls the advanced 16-camera security system, Sonos audio, automated shades, Lutron lighting, televisions, 5 GHZ Wi-Fi, and a dual central heating/cooling system with two climate zones in each room. A stunning Archimedean spiral staircase with oak risers and a cast iron filigree banister opens to a circular skylight, which allows abundant natural light to flood into the center of the home. Grand windows, astounding room proportions, and soaring ceilings throughout the residence create a bright, airy feel. Impeccable home finishes include an exterior facade built of the finest Indiana limestone, walnut hardwood flooring, Calacatta marble countertops, and extensive custom millwork.