The building has an Art Deco design with many lavish architectural finishes and a series of setbacks which taper toward the top floors.

[6] As a result of the land filling, 21 West Street was constructed without a basement,[9][10] which was "a decidedly rare feature" in New York City buildings, hence the need to import steam and electricity.

[5][6] The two buildings were constructed for different purposes and accordingly have different appearances; namely, the facade of 21 West Street is lighter in color than that of the Downtown Athletic Club.

[5] Starrett & van Vleck had already designed several New York City department stores, including the Lord & Taylor, Bloomingdale's, and Saks Fifth Avenue buildings.

[13][14] Architectural historian Anthony W. Robins described 21 West Street as "one of the area's handsome Art Deco towers".

[c][12][17] The facade of 21 West Street was designed with molded and oversized brick "to emphasize the structural lines and to enrich the texture of the materials".

[16][18] The polychrome design was influenced by Harvey Wiley Corbett's plan for the Master Apartments on the Upper West Side of Manhattan.

[19] At each setback and on the three lower levels, the parapets have various designs of molded brick to provide surface texture to the building's exterior.

[11] The arcade, storefronts, and main entrance contain decorative metalwork painted in silver and gold tones, which extend into the interior.

[11][12][21] 21 West Street contains a uniform fenestration pattern in contrast to the Downtown Athletic Club, which has several windowless floors.

[22] The lobby has a colorful marble mosaic on its floor, depicting the old street grid of Lower Manhattan in a style similar to a mariner's map.

[16] Since its conversion to an apartment building, the interior of 21 West Street has included a terrace on the 34th floor, a play area for children, and a fitness room.

The construction of the Interborough Rapid Transit Company's elevated railroad lines, and later the New York City Subway, had spurred the relocation of the area's residential population uptown in the late 19th and early 20th centuries; the tenements that developed at the edges of the Financial District were being demolished and replaced with office buildings.

[25] The building was owned by the 21 West Street Corporation, which had close ties with the maritime industry along the Hudson River.

[34] In 1997, the residential development and management firm, Rose Associates, announced plans to convert 21 West Street into a 293-unit apartment building called Le Rivage.