One of the world's tallest freestanding towers can be found in the city of Toronto, Canada. This large tower was made in collaboration with the Canadian National Railway and the Canadian Broadcasting Company in the 1970s. The people of Canada treasure this tower and fondly call it “Canada’s World Wonder.”
The base of the tower underwent construction on February 6, 1973. 62,000 tons of earth and rock were dug up in order to pour 57,000 tons of concrete. This concrete was used to support the 130,000 ton weight of the building. The base is 20 feet thick and 230 feet in diameter. This base was built in a hexagonal shape unlike normal circular towers. Using a concrete mold and a hydraulic jack, construction workers poured concrete into the mold, let it set, then used the hydraulic jack to lift the mold up approximately 20 feet each day. Because of this peculiar method of construction, the workers had to check everyday if the shaft of the tower was off its vertical center, using a 220 lb cylinder tied to a rope, to act as a plumb bob (a vertical indicator).
In 1976, once construction was completely finished, the CN Tower officially opened. Inside of this tower, there are two observation decks, a restaurant, and a nightclub. Glass elevators run up and down the side of the tower to take visitors from the ground floor to the top. On the lower level, there is an observation deck. This deck is made out of 2.5-inch thermal reinforced glass strong enough to withstand 38 tons. Looking down through this glass floor, there is a breathtaking view underneath it. Regardless of the reinforced glass, many were afraid of the glass breaking. Due to people’s fear, a carpet was laid on top of the glass.
Despite being a popular tourist attraction, it is not the main purpose of the CN Tower; instead, it serves as a television signal tower. An antenna crowns the top of the tower and was made from thirty-nine individual pieces of steel flown up using a Sikorsky helicopter. This shortened what would have taken a half a year to build, to only three and a half weeks.
Being one of the world’s largest towers, it naturally attracts visitors. 1.5 million people visit the CN Tower every year.
[Source: 100 Wonders of the World]