Apartment 6E at 790 Riverside Drive is spacious, with a Park Avenue apartment kind of flow--and size--,not what you might expect to find in a coop on 157th Street in lower Washington Heights, aka the Audubon Park Historic District. With predominantly north facing windows, it looks above the rooftops of the building across the street with magical city views and affords sightings of the George Washington bridge. The apartment has three bedrooms, two of which are currently furnished as libraries, two full bathrooms and another half bath which houses the vented washer/dryer. There are several unusually large public spaces, There's the huge living room (once laid out as a study and a side-by-side parlor), a full-sized dining room and a very gracious entry leading to a foyer that feels like a space in an art gallery. The very ample kitchen has a Sub Zero refrigerator, a Viking stove, a Bosch dishwasher and a universe of storage cabinets. There are two additional office spaces not shown in the photographs, originally staff bedrooms, one off the kitchen, and the other next to the laundry room. (see floorplan.) You can hide in this apartment, and it would be very tough to find you. Similarly grand is the building lobby, a block-long and clad in marble, with a doorman station at one end of it and a wheel-chair accessible door. The landmarked building has 24 -hour doormen, a live-in super, t handymen and porters. On the lobby level there's a package room, a laundry room, lockers and bike storage. The tree-filled neighborhood with meandering streets is sprouting restaurants, home-grown cafes, and bakeries and boasts increasingly open and friendly cultural institutions, including the Hispanic Society Museum and the American Academy of Arts and Letters, both of which now offer changing exhibitions and public performances, and are only a block from the back door of the Riviera. There is good transportation: the #1 train is a block away, the C and A trains are also nearby, as are the 4 and 5 bus. N-Y Presbyterian hospital and Columbia Medical Center are in the immediate neighborhood and City College and Columbia's Manhattanville campus are in a slightly farther away. The Hudson River Greenway down the street with its sports fields, playground and tennis courts, and there's also Riverbank State Park with an Olympic-sized pool, a track, skating and other facilities. /A