The Grinnell, a stately co-op in upper Manhattan, might just be the city’s best-kept secret — for now.

Replete with spacious homes, a strong sense of community and maintenance fees that are considerably less than in comparable buildings, the property stands in a sleepy corner of Washington Heights, at 800 Riverside Drive. It also rarely has openings — but house hunters and otherwise property-curious locals now have their best chance in years to become members of this exclusive, and under-the-radar, club.

In this 83-unit structure, where residents typically spend decades, there are now an unprecedented four apartments for sale. When they trade hands, they’ll mark the first sales at the Grinnell since 2020, according to StreetEasy, when only two units sold. In 2019, just three units found new owners.

“I don’t recall when [four homes] were on the market at the same time,” said Bruce Robertson, 71, a long-time Grinnell resident. Robertson, also a Compass broker, represents the six-room unit 8H, which listed on Saturday for $1.59 million — its first time up for sale in 45 years. Aptly called a “hidden treasure” in its marketing description, this top-floor spread has three bedrooms, a 23-plus-foot-long great room, a windowed kitchen with the original glass-fronted cabinetry, a formal dining room with wainscoting and views of the George Washington Bridge.

One day later, according to StreetEasy, a two-bedroom spread with one bathroom — and tony touches such as picture moldings — listed for $1 million with RE/MAX Sparrow Realty.

Among the other availabilities: Unit GRI, an eight-room duplex, which now asks $1.99 million after listing for $2.2 million in April. It boasts three bedrooms and two full bathrooms. Features include French doors, a wood-paneled dining room, original oak floors and cabinetry, and mirrored mahogany doors. (Instead of a traditional listing, this home — represented by Hauseit — is an assisted for-sale-by-owner offering.)

There’s even unit 2A — a 1,800-square-foot three-bedroom with French doors, crown moldings, and bonus spaces including a library, a foyer, a maid’s room and a pantry. It listed in September for $1.35 million — and is represented by Jamella Swift of Keller Williams NYC.

Occupying a full triangle-shaped block between 157th and 158th streets — and Riverside Drive and Edward Morgan Place — the Grinnell offers homes of a bygone New York era. The smallest apartment has five rooms and measures 1,100 square feet; the largest has more than 10 rooms and spans 2,700 square feet. Built in 1911 and designed by architects Schwartz & Gross, it’s a history-rich standout with a Mediterranean-style façade, a porte-cochere entryway to an interior courtyard — and other classic interior details including hardwood floors, leaded glass transoms and 10-foot ceilings. Amenities include a gym, a bike room and a rooftop terrace.

Apart from the grande-dame glamour and million-dollar asking prices, many New Yorkers don’t know it’s a Housing Development Fund Corporation (HDFC) co-op — meaning it’s part of the city’s affordable housing stock and subject to certain income restrictions for home purchases. It’s one of the most successful co-ops of its kind, and that “has worked well to maintain the Grinnell’s large infrastructure over the years,” said Robertson.

That said, the Grinnell is the uptown early-20th century apartment building fit for savvy New York royalty who, with the proper income requirements, can act now to get a coveted deal. It’s no surprise residents end up staying put.

“People who purchase in the Grinnell don’t move because it’s a wonderful place to live,” said Robertson, who’s also a former member of the building’s board and has sold 10 units in the building over the years.

Robertson has lived in a two-bedroom, one-bathroom spread with his wife, also a real estate broker, for the past 22 years. They found the apartment on a whim after getting priced out of their Upper East Side condo and immediately knew the building was special. He loves the south-facing windows, bright light, solid construction, high ceilings, hardwood floors and the quiet.

“All in all, it’s hard to encapsulate how the Grinnell is so special and how that came to be. Mostly because it truly is a community of cohesive residents, many families who’ve grown, now being replaced by young families, who care about each other,” Robertson said. “We don’t always agree about issues facing any 102-year-old landmarked building of its size and scope. But we work through them and are proud of a beautiful structure that looks and feels like living in a castle, in a bucolic-feeling area with wonderful neighbors in other comparable buildings.”

Other long-time residents agree it’s a building with a lovely spirit.

Bruce Kanze, 74, an adjunct lecturer at the nearby City College of New York, moved to the Grinnell in December 1977 and lived in apartment 3B. He moved to 8F in March 1982, an eight-room, two-bedroom, two-bathroom apartment, with his wife and three kids, where he’s lived ever since.

“There’s a sense of belonging to a community, and we love our neighbors,” Kanze said. He recalled fond memories of climbing the mulberry tree in front of the building and picking berries with his daughters, of setting up summer lemonade stands with them — and of crab fests with the neighbors. “We’d buy bushels and cover the tables with paper bags and see who had the highest pile of crab shells,” he added.

But another reason why people stay so long in the Grinnell is because of its HDFC title. It’s one of 1,100 HDFC co-ops in the city, where residents are shareholders and own the building collectively. The status dates to 1982 when residents successfully bought the Grinnell from the city after a campaign that included the slogan, “Buildings for People, Not for Profit.” Apart from the tony interiors and like-minded community, part of the conditions for ownership include a flip tax, which also keeps residents put. The funds from it go towards the building’s capital reserve.

In addition to the income restrictions, a real-estate tax abatement makes the maintenance less than other co-ops of comparable size and stature. By contrast, a four-room, 2,000-square-foot apartment at 116 Pinehurst Ave. will set you back $1.58 million with $3,400 a month in maintenance. Similarly, a three-bedroom co-op in the century-old Riviera across West 157th Street from the Grinnell is going for $1.79 million with $2,174 a month in maintenance. Robertson’s $1.59 million listing, for instance, has $1,448 per month in maintenance. Both unit GRI and 2A have $1,450 monthly fees, StreetEasy shows.

Wayne Benjamin, 64, an architect who bought a 1,300-square foot, two-bedroom co-op in the Grinnell in 1987 for just $85,000 — about $228,000 today — has no plans to go anywhere. He enjoys cooking in his full-sized kitchen and listening to music on his vinyl record player — or jazz on an old-fashioned FM radio with a pair of speakers. He also enjoys rare New York City cross-ventilation, as every room in the apartment has exposures — so he can open the dining room windows, which face the courtyard, and the French doors and windows in the living room across the hallway, which face the street, and enjoy breezes year-round.

But in the end, it’s the people.

“It comes down to what’s important,” Benjamin said about the pull the Grinnell has keeping him there. “There are things that you share in common with others — common concerns and interests that you come together to address. That is what creates the sense of community that can make a building or neighborhood a vibrant wonderful place to live.”