The CN Tower (in French: "Tour CN") is a 553.33 m-high (1,815.4 ft) concrete communications and observation tower in Downtown Toronto, Ontario, Canada. Built on the former Railway Lands, construction on the CN Tower began on February 6, 1973. It was completed in 1976, opening to the public on June 26, and became the world's tallest free-standing structure and world's tallest tower at the time. It held both records for 34 years until the completion of Burj Khalifa and Canton Tower in 2010; However, the CN Tower remains the tallest free-standing structure in the Western Hemisphere, a signature icon of Toronto's skyline, and a symbol of Canada, attracting more than two million international visitors annually.
Its name "CN" originally referred to Canadian National, the railway company that built the tower. Prior to the railway company's privatization in 1995, it transferred the tower to the Canada Lands Company, a federal Crown corporation responsible for real estate development. Since the name CN Tower became common in daily usage, the abbreviation was eventually expanded to Canadian National Tower or Canada's National Tower. However, neither of these names is commonly used.
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). Each of the three elevator shafts are lined with glass, allowing for views of the city as the glass-windowed elevators make their way up the Tower. The stairwell was originally located in one of these angles (the one facing north), but was moved into the central hollow of the Tower; the Tower's new fifth and sixth elevators were placed in the hexagonal angle that once contained the stairwell. On top of the main concrete portion of the Tower is a 102-metre (334.6 ft) tall metal broadcast antenna, carrying TV and radio signals. There are three visitor areas: the Glass Floor and Outdoor Observation Terrace which are both located at an elevation of 342 metres (1,122 ft), the Indoor Lookout Level (formerly known as "Indoor Observation Level") located at 346 metres (1,135 ft), and the higher SkyPod (formerly known as "Space Deck") at 446.5 metres (1,465 ft), just below the metal antenna.
The Main Pod (seen above) is seven storeys, some of which are open to the public. Below the public areas — at 338 m (1,108.9 ft) — is a large white donut-shaped radome containing the structure's microwave receivers. The glass floor and outdoor observation deck are at 342 metres (1,122.0 ft). The glass floor has an area of 24 m2 (258 sq ft) and can withstand a pressure of 4,100 kilopascals (595 psi). Some people experience acrophobia when standing on the glass floor and looking down at the ground 342 m (1,122.0 ft) below. In 2008, one elevator was upgraded to add a glass floor panel, believed to have the highest vertical rise of any elevator equipped with this feature. The Horizons Cafe and the lookout level are at 346 metres (1,135.2 ft). The 360 Restaurant, a revolving restaurant that completes a full rotation once every 72 minutes, is at 351 m (1,151.6 ft). When the tower first opened, it also featured a disco named Sparkles, billed as the highest disco and dance floor in the world. For those daring and brave enough, on August 1, 2011, the CN Tower opened the EdgeWalk, an amusement in which thrill-seekers can walk on and around the roof of the main pod of the tower at 356 m (1,168.0 ft), which is directly above the 360 Restaurant. It is the world's highest full-circle, hands-free walk. Visitors are tethered to an overhead rail system and walk around the edge of the CN Tower's main pod above the 360 Restaurant on a 1.5 m (4.9 ft) metal floor. Not surprisingly, the attraction is closed throughout the winter season and during periods of electrical storms and high winds. The SkyPod was once the highest public observation deck in the world until it was surpassed by the Shanghai World Financial Center in 2008. On a clear day, it is possible to see up to 100 to 120 km (62 to 75 mi) away, to the city of Rochester across Lake Ontario in the United States, the mist rising from Niagara Falls, or the shores of Lake Simcoe.
A metal staircase reaches the main deck level after 1,776 steps, and the SkyPod 100 m (328 ft) above after 2,579 steps; it is the tallest metal staircase on Earth. These stairs are intended for emergency use only and are not open to the public, except for two times per year for charity stair-climb events. The average climber takes approximately 30 minutes to climb to the base of the radome, but the fastest climb on record is 7 minutes and 52 seconds in 1989 by Brendan Keenoy, an Ontario Provincial Police officer.
In 1995, the CN Tower was declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers. It also belongs to the World Federation of Great Towers, where it holds second-place ranking.