These million-dollar luxury condos used to be the storied offices of a big Wall Street bank. See inside the transformation.

• Developer Macklowe Properties converted a Financial District office building into a condominium.
• The 1.25 million-square-foot tower is the largest office-to-residential conversion in New York City.
• The New York landmark was completely reconfigured inside, including removing 30 elevators.

An Art Deco office tower that's been an icon on the Lower Manhattan skyline since 1931 is getting a new life — as $1 million-plus condos.

Built as the headquarters of the Irving Trust Company in 1931, One Wall Street is now home to the largest office-to-residential conversion project in New York City history. 

Developer Macklowe Properties took on the challenge of creating 566 luxury residences while maintaining the original Art Deco aesthetic of the 1.25 million-square-foot building. 

Lilla Smith, the director of architecture and design at Macklowe Properties, said she even took extra steps like sourcing limestone from the same quarry in Indiana that was used during the original building process.

Once most of the inside was gutted, it made for a clean canvas for Smith to reconstruct office space to residential, she said.

"We really did a complete redo," Smith told Insider. "We almost had a clean slate for doing our layouts."

The 566 residences vary from studios to four-bedroom units and range in price from $1.13 million to $12.75 million, not including the penthouse. Look inside the building's transformation.

Built for the Irving Trust Company in 1931, One Wall Street is now home to the largest office-to-residential conversion in New York City.

The Irving Trust Company was acquired by the Bank of New York in 1988.

The building now has 566 condos with layouts that range from studios to four bedrooms.

According to Smith, the developers restored or repurposed brass and bronze on many of the fixtures, including the revolving doors.

An entrance on Broadway was sealed in the 1960s. During the renovation, Macklowe recreated the entrance for residents.

Many office mainstays, like security gates, were removed to make for a more welcoming entry experience.

Smith was inspired to keep the Art Deco style when designing the lobby.

"There's all this fluting on the metal work, fluting on the stone and wood paneling," Smith said, speaking of the building's Art Deco touches. "We've also incised patterns on the glass and on the woodwork."

Thirty elevators were removed during the redesign. The 10 that remain were centralized in the building.

After all, Smith pointed out, the elevators no longer needed to meet the needs of employees during rush hours and lunchtime.

The Art Deco doors from some elevators were restored and repurposed as decor in Whole Foods, one of the building's commercial tenants.

One Wall Street was constructed before air conditioning with operable windows — a rarity for later-built office buildings.

Converting some offices can be difficult because their layouts result in jagged or awkward floor plans for the eventual apartments.

"We do not have quirky layouts because we took the effort to redo the core," Smith said of the condos and removing the elevators. "It's not like a 1960s office building on Sixth Avenue, which is just not going to be conducive to being repurposed and converted from commercial to residential."

She added, "The building lent itself to the change in use."

Because One Wall Street is a New York City landmark, the facade had to remain mostly the same. But its terraces got a major makeover.

Some of the terraces are now common space for residents and others are private outdoor space for condos.

The 38th floor is home to some of the resident amenities, called The One Club, including a 75-foot swimming pool with a wraparound terrace.

The 39th floor is home to a shared outdoor terrace with downtown and New York Harbor views...

...as well as a restaurant for residents and their guests.

Keeping the spirit of the former office building alive, there is a coworking space with conference rooms and a coffee bar.

The Red Room on the ground floor was formerly used as a banking room. It has been closed off to the public until now.

The room was designed by Hildreth Meière in the Art Deco style with walls that feature 13,000 square feet of mosaic tiles in hues of red, orange, and gold, according to Architectural Digest.

Restoration experts were able to restore the brass of the entrance doors and windows as well as clean the decades-old tile.

"It's got its luster back," Smith said. "Every mosaic tile was cleaned."

Architectural Digest also noted that during the renovation process, an unopened box of several thousand original tiles was unearthed in the building's basement.

Macklowe Properties had to add a sprinkler system to the room in case of fires.

Luckily some of the lighting fixtures in the ceiling were able to be used for the system rather than creating new holes, Smith said.

French department store Printemps will open its first US outpost across 54,000 square feet in the building, including the Red Room.