21 East 81st Street presents a rare and highly unique opportunity on one of the Upper East Side's most coveted townhouse blocks, perfectly positioned between Fifth and Madison Avenues. Built in 1899 by renowned architects Welch, Smith & Provot, this 20-foot-wide Neoclassical limestone townhouse spans approximately 8,600 square feet across four stories, crowned by a mansard roof. Grand ceiling heights, significant original architectural detail, and wood-burning fireplaces in nearly every room define the interiors, while an elevator services all levels. Currently configured as a two-family residence-an owner's quadraplex with income producing duplex -the home offers exceptional flexibility and long-term potential which can also can easily be converted to a single family.