A once-in-a-generation opportunity to own a storied piece of the Hamptons' "Gold Coast," this 3.6-acre waterfront masterpiece is perched high atop a bluff with 260 feet of private beach frontage, offering breathtaking views of Great Peconic Bay, Robins Island, and the North Fork. Once home to the original 1896 Hampton Bays bluff-side "Cottage," known as Mostly Hall, this historic site now presents a rare, shovel-ready opportunity for a modern estate of timeless elegance. Designed by renowned architect Brian Brady, the 5,700 sq. ft. residence seamlessly blends classic Hamptons charm with contemporary luxury. With all permits secured and materials on-site, your waterfront dream home is ready to begin. This estate is designed for elevated living, with an expansive layout that maximizes both comfort and style. The lower level includes a home gym, recreation room, guest suite, walk-in cedar closet, full bath, laundry, and ample storage. The ground level boasts a chef's kitchen with a butler's pantry, breakfast room, dining room, living room with a grand fireplace, screened porch, garden room, mudroom, full bath, and the option for a first-floor primary suite, with elevator access to all three floors. On the second level, the primary suite offers breathtaking water views, accompanied by three additional en suite bedrooms and a sitting room with a private balcony overlooking the bay. Designed for the ultimate waterfront lifestyle, the property features a brand-new bulkhead with stairs leading directly to your private beach, as well as pending dock approval for direct water access and boat docking. Outdoor amenities include a pool with spa, a 450 sq. ft. pool house, expansive wraparound decks perfect for entertaining, and a two-car garage. Additionally, the estate includes an adjacent 1-acre lot, providing space for a guest house and tennis court. A seamless blend of history and modern luxury, this extraordinary property is ready for immediate development-secure your waterfront legacy today.