At a windy altitude of 110 storeys, marvels of engineering and nerves of steel are required for even the most ordinary task, like keeping over 13 acres of glass of the twin towers, clean.
There are 43,600 windows in both towers, which are cleaned by custom-built devices, and by hand.
The World Trade Center houses more than 430 businesses from 28 different countries. There are 198 elevators that serve the 50,000 people who work in the North Tower and South Tower.
The world famous twin towers attract 1.8 million visitors on average each year, as well as iconic film characters such as Spiderman and, King Kong.
On the 106th and 107th floors of the North Tower is Windows on the World, a spectacular venue for dining, entertainment, and celebrations, which is served by 450 employees. The restaurants occupy more than an acre of floor area, and offer dining rooms for two to 2,000 guests.
Equally notable is The Mall at the World Trade Center on the concourse level, which contains eateries and 80 retailers; it is the largest indoor shopping center in Downtown Manhattan. The mall also serves as a point of access to the subway station on the A, C, and E trains.