A Landmark Residence with Historic Grandeur and Modern Refinement. Built in 1879, this 20-foot-wide Neo-Grec masterpiece stands as a striking example of period architecture, distinguished by its commanding facade and its enviable placement on East 67th Street between Madison and Park Avenues-one of the Upper East Side's most sought-after blocks. Just a short stroll from Central Park, the home offers an extraordinary combination of historic elegance and modern comfort. Spanning five stories plus a dramatic mezzanine, the residence encompasses approximately 8,270 square feet of interior living space, thoughtfully enhanced by 1,560 square feet of outdoor retreats spread across four private terraces. An additional 2,000-square-foot excavated lower level, complete with elevated ceiling heights, adds impressive versatility for recreation, wellness, or wine storage. Currently configured as a single-family residence with a ground-floor professional suite, the home offers exceptional adaptability. The professional space can remain separate, continue as a revenue-producing element, or be seamlessly integrated into the main residence to expand the home's living quarters. The interiors are designed to balance grandeur and livability. The parlor floor evokes a loft-like openness, featuring expansive living and dining areas anchored by a showpiece chef's kitchen with direct access to a large private terrace-ideal for entertaining on an intimate or grand scale. The seven-bedroom layout is crowned by a top-floor primary suite, boasting a marble-clad bathroom, abundant storage, and an adjoining double-height library/study that opens to a private terrace with roof access. Additional features underscore the property's caliber: a sweeping central staircase, a newly installed commercial-grade elevator servicing every level, radiant heated floors, a soundproofed media room, advanced mechanical systems, and a comprehensive security system. With its rare scale, impeccable design, and prized location, 51 East 67th Street offers an opportunity to own one of the Upper East Side's great private houses-surrounded by world-class shopping, fine dining, museums, and cultural landmarks.