Widely regarded as one of the boldest engineering achievements of its era, the CN Tower rises 553 metres above downtown Toronto and was long celebrated as the tallest freestanding structure in the world, a distinction it held for more than three decades. Its slender concrete shaft supports a rounded main pod containing observation levels and a revolving restaurant, with a tapering steel mast fixed to the top. Remarkably, the graceful outline first sketched in the early 1970s is still the profile that greets visitors today.

The motivation for the tower's construction came largely from a problem with the airwaves. Through the 1960s, the growing cluster of tall office buildings in the city centre had begun to block television and radio signals, leaving many households with poor, unreliable reception. Engineers argued that a single antenna raised well above the rooftops would solve the trouble at a stroke, while the railway company behind the plan also hoped the structure would showcase the strength of Canadian industry. The project promised to be difficult, since the site sat on soft, water-logged ground and the finished tower would have to stand firm against fierce winds.