After nearly a decade of design and development work, what is being billed as “the world’s most expensive home” is finally ready for its close-up. Set on a five-acre parcel in the posh Los Angeles enclave of Bel Air—and aptly named The One—the 105,000-square-foot property’s interiors have remained a closely guarded secret. Until now. AD has been an exclusive look at what’s inside this record-setting property—and the design and aesthetic minds that made it happen.

Surrounded on three sides by a moat and a 400-foot-long jogging track, the estate appears to float above the city. Completed over eight years—and requiring 600 workers to build—the home was designed by architect Paul McClean and interior designer Kathryn Rotondi, who were enlisted by owner and developer Nile Niami to help it live up to its reported $340 million price tag.

“This project felt exciting and simultaneously intimidating,” says McClean. But the home’s impressive site and his long-standing relationship with Niami persuaded McClean to not just take on the project but “create something unique and spectacular.”

And McClean certainly has delivered.

With its 26-foot-high ceilings, the home’s main entrance leads to an array of gathering areas with panoramic 360-degree views of the Pacific Ocean, downtown Los Angeles, and the San Gabriel Mountains. The entry area is filled with water, along with a sculpture and bridge. “Water is something we often use in our design process because it allows for a sensory change that helps you adjust to your surroundings,” says McClean.

The use of black, white, and gray throughout the home was based on Niami’s desire to have a neutral palette that would allow the landscape and panoramas to shine.

Drawing inspiration from the surrounding environment and history of Los Angeles modernism, McClean has connected the home’s inside with outside “to provide that quintessential L.A. living but on a bigger scale,” he describes. “To allow the home to feel livable, we separated the entertainment spaces from the living areas. [The former] are located at the lower level [and] this creates a plinth for the rest of the house to sit on and reduces [its] apparent mass.”

Beyond the eye-catching design are the home’s equally jaw-dropping stats. There are 42 bathrooms, 21 bedrooms, a 5,500-square-foot master suite, a 30-car garage gallery with two car-display turntables, a four-lane bowling alley, a spa level, a 30-seat movie theater, a “philanthropy wing (with a capacity of 200) for charity galas with floating pods overlooking Los Angeles, a 10,000-square-foot sky deck, and five swimming pools.

Along with Niami, Rotondi, founder of KFR Design, worked on the interior design to shape distinctive spaces that flow into one another despite the grandness of the house. “I was really drawn to ‘wow factor’ elements in the hospitality sector” for inspiration, says Rotondi, who looked to top luxury hotel brands such as Aman, Bulgari and Baccarat. Meanwhile, the home’s color palette, soft textures, and lighting are an ode to the Tom Ford boutique on Rodeo Drive, a favorite of Niami and McClean.

Thanks to a collaboration between Creative Art Partners and Art Angels, the property features an impressive collection of art, including a butterfly installation by Stephen Wilson on the lower level and a Niclas Castello custom panel in black and silver in the office. There is also a sizable collection of bespoke furniture pieces from byShowroom.

Due to recently approved city ordinances, a house of this magnitude will never again be built in Los Angeles, which means The One will truly remain one of a kind. “This project has been such a long and educational journey for us all,” McClean notes. “It was approached with excitement and was thrilling to create, but I don’t think any of us realized just how much effort and time it would take to complete the project.”

Now it’s time to find the perfect buyer for it. Branden and Rayni Williams of The Beverly Hills Estates, along with Compass’s Aaron Kirman, will have the listing.