The CN Tower is a 553.3 m-high concrete communications and observation tower in downtown Toronto, Ontario, Canada. Its name “CN” referred to Canadian National, the railway company that built the tower.

The CN Tower held the record for the world’s tallest free-standing structure for 32 years, from 1975 until 2007, when it was surpassed by the Burj Khalifa, and was the world’s tallest tower until 2009 when it was surpassed by the Canton Tower. It is currently the tenth-tallest free-standing structure in the world and remains the tallest free-standing structure on land in the Western Hemisphere.

The CN Tower consists of several substructures. The main portion of the tower is a hollow concrete hexagonal pillar containing the stairwells and power and plumbing connections. The tower’s six elevators are located in the three inverted angles created by the Tower’s hexagonal shape (two elevators per angle).

The main deck level has seven storeys, some of which are open to the public. Below the public areas—at 338 m —is a large white donut-shaped radome containing the structure’s UHF transmitters. The glass floor and outdoor observation deck are at 342 m. The glass floor has an area of 24 m2 and can withstand a pressure of 4.1 megapascals. The floor’s thermal glass units are 64 mm thick, consisting of a pane of 25 mm laminated glass, 25 mm airspace and a pane of 13 mm laminated glass.

In 2008, glass panels were installed in one of the CN Tower elevators, which established a world record (346 m) for highest glass floor panelled elevator in the world.

According to Wikipedia