5. Waterfall Mansion
Waterfall Mansion—an 1899 carriage townhouse on the Upper East Side—is a museum-like event space that draws its name from a 20- by 24-foot indoor waterfall. The five-floor home spans 13,000 square feet and includes a third-floor garden terrace and a roof deck. It opened in May for events and has been used for product launches, nonprofit dinners, and receptions.