Located on one of Carnegie Hills most coveted tree-lined townhouse blocks just off Park Avenue, 117 East 91st Street is a distinguished four-story brownstone that embodies the timeless elegance and architectural grandeur of New Yorks Gilded Age. Spanning approximately 3,300 square feet, this exceptional residence offers four bedrooms, three-and-a-half baths, gracious entertaining spaces, and a private garden oasis in the heart of the Upper East Side. Rich in original detail and historic charm, the home showcases beautifully preserved inlaid wood floors, marble mantels, magnificent pocket doors with etched glass, and intricate moldings, lending character throughout. Soaring ceilings and generous proportions create a remarkable sense of scale rarely found in Manhattan townhouses today. The impressive parlor level, featuring approximately 11-foot ceilings, is perfectly suited for both elegant entertaining and comfortable daily living. A grand formal living room overlooks the garden and is bathed in natural light, while a separate home office provides a quiet and refined workspace. On the garden level, the home is thoughtfully arranged for effortless living and entertaining, with a kitchen, breakfast room, and formal dining room opening directly onto the private garden creating a seamless indoor-outdoor experience rarely found in the city. The sun-filled primary bedroom enjoys southern exposure and charming bay windows with picturesque tree-lined views, complemented by a built-in window seat that enhances the rooms warmth and character. The flexible upper-floor layout offers exceptional versatility. The entire third floor can function as a luxurious primary suite with dressing room, or alternatively as two bedrooms with the potential to create an additional en-suite bath. The fourth floor currently offers two additional bedrooms and two baths. Lovingly maintained over the years, the residence offers a rare opportunity to thoughtfully personalize and enhance a classic Carnegie Hill townhouse while preserving its extraordinary architectural integrity and historic character. Modern infrastructure improvements include a new HVAC system, upgraded electrical wiring, newly installed recessed lighting, new hardwood floors in the parlor room study, and a fully renovated fourth floor bathroom, all providing contemporary comfort alongside timeless pre-war craftsmanship. Beyond its existing beauty and scale, the property also presents exceptional potential for future expansion. There is the opportunity to add another level, create an extension, or both. The owners have completed a comprehensive set of DOB-filed architectural, structural, MEP, and geotechnical plans, offering a valuable foundation for future enhancements. The breakfast room, the dressing room, and the garden are virtually staged.