The Twin Towers were essentially two vertical cities. Each tower rose 110 stories and held dozens of major corporations, government offices, restaurants, observation decks, and the infrastructure needed to support roughly 50,000 workers and 200,000 daily visitors. Below ground, six basement levels housed a commuter rail station, a vast shopping concourse, and utility systems that kept the complex running. Here’s what filled those buildings from bottom to top.
Six Basement Levels Below the Plaza
The World Trade Center sat inside a massive concrete structure known as the “Bathtub,” a retaining wall that held back the Hudson River and created six underground levels beneath the plaza. These subterranean floors contained parking garages, storage areas, mechanical equipment, and a sprawling retail concourse with shops and restaurants that connected the towers to the surrounding streets.
The deepest level, B6, held a station for the PATH commuter train, which carried passengers under the Hudson River between Manhattan and New Jersey. This rail connection made the World Trade Center a transit hub, not just an office complex. Tens of thousands of commuters passed through the PATH station every weekday. The lowest level sat below the waterline of the river, which became a serious engineering concern when the buildings collapsed and water began flowing through the damaged tunnel toward Exchange Place Station in Jersey City.
The Elevator System That Made It Work
No one could ride a single elevator from the ground floor to the top. The towers used a “sky lobby” system, a design innovation that made 110-story office buildings practical. Express elevators carried passengers from the ground floor to sky lobbies on the 44th and 78th floors of each tower. From those transfer points, local elevators served the surrounding floors. This approach dramatically reduced the number of elevator shafts needed, freeing up rentable floor space on every level. The system divided each tower into three vertical zones, each functioning almost like a separate building stacked on top of the one below.
Who Worked in the North Tower
One World Trade Center, the North Tower, housed a mix of financial firms, insurance companies, law offices, and government agencies. The Port Authority of New York and New Jersey, which built and owned the complex, kept its own offices there. Marsh & McLennan Companies, a major insurance brokerage, occupied several floors in the upper section of the building. Cantor Fitzgerald, a bond trading firm, was headquartered on floors 101 through 105, making it one of the highest-placed tenants in the tower. The firm lost 658 employees on September 11, nearly its entire New York workforce.
Other significant tenants included Bank of America, the Japanese financial group Dai-Ichi Kangyo, the law firm Sidley Austin Brown & Wood, and Empire Blue Cross and Blue Shield. The upper floors also held one of the most famous restaurants in New York City.
Who Worked in the South Tower
Two World Trade Center, the South Tower, leaned even more heavily toward finance. Morgan Stanley, the investment bank, was the largest single tenant in the entire complex, occupying floors throughout the building. Aon Corporation, another insurance and consulting giant, had a major presence on the upper floors. Fiduciary Trust Company International, Keefe Bruyette & Woods (a banking-focused brokerage), and the New York Stock Exchange also kept offices there. Verizon and Xerox rounded out the corporate roster.
The South Tower also held the Top of the World Trade Center Observatories on the 107th floor, the main public observation deck that drew tourists year-round.
The Surrounding Buildings
The World Trade Center was not just the two towers. It was a complex of seven buildings. Six World Trade Center served as the U.S. Customhouse and held offices for the United States Customs Service, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), the Department of Commerce, and the Department of Labor. The ATF maintained vaults in the building filled with tactical weapons and firearms. Seven World Trade Center, the 47-story tower that also collapsed on September 11, housed Salomon Smith Barney, the U.S. Securities and Exchange Commission, Standard Chartered Bank, and a field office of the U.S. Secret Service.
Windows on the World
The 106th and 107th floors of the North Tower held Windows on the World, a restaurant complex that was one of the highest-grossing dining destinations in the United States. “Windows on the World” was actually an umbrella name for several distinct venues spread across the 107th floor: the main fine-dining restaurant, a smaller wine-focused restaurant called Cellar in the Sky, the City Lights Bar, the Statue of Liberty Lounge, a small-plates restaurant called the Hors d’Oeuvrerie, and the Hudson River Suites for private events.
The 106th floor operated during the day as an exclusive luncheon club with roughly one thousand members, most of them professionals who worked in the building or nearby. In the evenings and on weekends, the space converted to public restaurant use. The views stretched across all five boroughs, New Jersey, and on clear days, far beyond.
Cooling, Water, and Mechanical Systems
Keeping the towers comfortable required industrial-scale infrastructure. The original World Trade Center used a river water cooling system that pumped water from the Hudson River through a pipeline, passed it through heat exchangers to absorb warmth from the building’s air conditioning systems, and discharged it back into the river at the North Cove of Battery Park City. At peak capacity, the original system could move well over 100,000 gallons per minute. Water entering the pipeline ranged from the low 40s in winter to the high 70s in summer. Mechanical floors, stacked at intervals throughout each tower, held the heavy equipment for heating, ventilation, air conditioning, and electrical distribution. These floors had no tenants and were recognizable from the outside by their distinct window patterns.
Art Throughout the Complex
The World Trade Center housed a significant public art collection, curated by the Port Authority and displayed in lobbies, mezzanines, and the outdoor Austin J. Tobin Plaza between the towers. The most recognizable piece was “The Sphere,” a massive bronze sculpture by Fritz Koenig that stood at the center of the plaza fountain. It survived the collapse in damaged form and is now displayed in Liberty Park adjacent to the memorial site.
Alexander Calder’s bright red steel sculpture, known as “Three Wings” or “Bent Propeller,” sat on an elevated walkway near Seven World Trade Center. Inside the South Tower’s mezzanine hung a large tapestry by Joan Miró, one of the most valuable single artworks in the complex. A Louise Nevelson sculpture called “Sky Gate, New York” occupied another interior space. Works by Roy Lichtenstein, Frank Stella, Al Held, and James Rosati were displayed in lobbies and public corridors. A granite-and-water memorial by Elyn Zimmerman occupied a section of the plaza. Most of these works were destroyed on September 11.
The sheer density of what filled the Twin Towers and their surrounding buildings reflects their role as more than office space. They functioned as a self-contained district: transit hub, financial center, government complex, tourist attraction, art gallery, and one of the most celebrated dining destinations in New York, all compressed into 16 acres of lower Manhattan.