A mixed-use five-story building is on the market for $5.75 million at 231 East 60th Street in Manhattan. : This mixed-use five-story building on the Upper East Side, to be delivered vacant, has been home to the Davis & Langdale art gallery on the parlor, ground floor and lower level. Above it are three floor-through market-rate apartments. Mature trees and a fountain covered with ivy are in its 20-by-50-foot garden. The building, two doors east of Serendipity 3 restaurant and up the block from the Roosevelt Island tram, also offers 2,900 square feet in air rights.