The building stands more than 1,815 feet tall - that's over six football fields standing end to end - and is visited by about two million people every year. Located at 1,122 feet is the outdoor observation deck, at 1,136 feet is a café and indoor observation deck, and if you go just a bit higher to 1,150 feet, you'll find an award-winning rotating restaurant. At the very top is the Sky Pod, the world's highest public observation deck.

The World's Tallest Building, 1976

In the early 1970s the city of Toronto's building boom created an interesting problem. Because the transmission towers of the city's TV stations weren't tall enough, many people weren't receiving high quality television reception. Canadian National decided to solve that problem and in 1972 conceived of a tower that would not only allow for uninterrupted broadcast signals, but would also be the tallest building in the world.

The engineers had a huge challenge. They had to design a tower with a base that was far underground. They tested the soil to see how it would react to changes in hydrostatic pressure and on February 6, 1973, they set to work. Before contractors could pour the concrete and steel foundation, 62,000 tons of earth had to first be removed. The base of shale was then smoothed by both hand and machine and a foundation 22 feet deep, containing 9,200 cubic yards of concrete, was poured. In spite of the massive scope for this groundwork, it took only four months from start to finish to complete the foundation.

Next came the building itself. In August of 1974, workers began using steel and wood brackets that had to be lifted up the sides of the tower by hydraulic jacks in order to complete the building. The tower was topped by an observation deck, constructed of brackets bolted to tensioned steel bars, concrete and a three feet high compression ring. All in all, it took 40 months for the 1,537 construction crew members working 24 hours a day for five days a week to complete the CN Tower.

Over that time concrete contractors poured 53,000 cubic yards of concrete, accounting for much of the building's 130,000 ton weight. The total cost for this project was $63 million, which would be about $300 million today.

The building stands more than 1,815 feet tall - that's over six football fields standing end to end - and is visited by about two million people every year. Located at 1,122 feet is the outdoor observation deck, at 1,136 feet is a café and indoor observation deck, and if you go just a bit higher to 1,150 feet, you'll find an award-winning rotating restaurant. At the very top is the Sky Pod, the world's highest public observation deck.

The CN Tower has been recognized as the world's tallest building by the Guinness Book of World Records and includes the world's highest wine cellar and longest metal staircase. The tower was named one of the Seven Wonders of the Modern World by the American Society of Civil Engineers in 1995.