A nondescript Gramercy Park walk-up is considered to be Manhattan’s oldest intact apartment building. And now, it’s for sale.

The $15 million listing at 129 E. 17th St. would be the first time the historic property has sold in more than two decades, according to city records. Listing agent Haley Hasho of Exodus Capital represents the sellers.

The property was completed in 1879, and at $20,000 — about $650,000 today — cost twice as much as a typical tenement of its size. At the time of its completion, it housed five families with two bedrooms per apartment. Today, No. 129 hosts five units in total, including a ground floor office space, plus a roof deck.

The French Gothic apartment building was constructed in 1887. ALEX STANILOFF

Its interiors, restored in 1990, still maintain much of their Victorian charm. Emmy Park for NY Post

The red-brick and brownstone facade of No. 129, pictured in the 1940s. NYC Municipal Archives

The red circle shows the building, and the lovely block, in 1938. George D. Chill/ The New York Public Library Digital Collections. 1938

The unassuming brick property nestled between Irving Place and Third Avenue represents a pivotal turning point in Manhattan living, constructed at a time when New Yorkers either lived in crammed housing tenements or in stately mansions. The Dakota, built in 1884 on West 72nd Street, has long been known as the first luxury apartment building in the US.

The late 19th-century emergence of the in-between — attractive multi-family housing for middle- and somewhat upper-class renters — reshaped how New Yorkers lived together.

The architect of No. 129, Napoleon LeBrun, is behind many of the city’s similarly French Gothic firehouses and some early skyscrapers, including Flatiron’s Metropolitan Life Insurance Company Tower. LeBrun was commissioned by Jane Scott, a widowed woman outside of the real estate industry, according to a 1990 New York Times profile of the restored property.

The multi-family building is ripe for a condo conversion. ALEX STANILOFF

Dark green French doors complete the foyer. Emmy Park for NY Post

A curving green staircase connects the five-story walk-up. Emmy Park for NY Post

The four apartment units feature woodburning fireplaces and hardwood floors throughout. Emmy Park for NY Post

A large bay window overlooks East 17th Street. Emmy Park for NY Post

LeBrun’s five-story red brick and brownstone building still contains much of its Victorian charm. Previously advertised units within boasting marble mantelpieces, pocket doors, oversized windows and rich hardwood flooring throughout.

Its unaltered exteriors and interiors earned No. 129 the distinction of the city’s oldest extant apartment building in 1957, when the 1870s-era Stuyvesant apartments were bulldozed. Before its fall, Stuyvesant was believed to be “the first genteel apartment house in a city then divided between private houses and tenements,” the Times reported.

The building’s four market-rate units are attractively large for the Manhattan market. Three out of the four are three-bedrooms, according to Hasho, including two duplexes. A one-bedroom penthouse completes the set.

The property last sold in 2005 for $1.79 million, according to city records. It is currently operated by two business partners going their separate ways, Hasho said.

A double-door apartment entrance. Emmy Park for NY Post

Two out of four rentals at No. 129 are currently vacant. Emmy Park for NY Post

Rents throughout the building reached five digits in recent years. Emmy Park for NY Post

Large windows flood each unit with natural light. Emmy Park for NY Post

The current owners have been able to achieve lofty rent prices for the Gramercy Park pad. The building most recently secured a $18,500-a-month lease on a three-bedroom duplex in 2024, according to StreetEasy.

Now No. 129 is set for a slated for a new chapter. Hasho advertised the walk-up as a conversion opportunity, to be altered into condos or a single-family residence.

“I think the likely suspects are the developers who are going to sell out the units for condos,” Hasho told The Post.