CN Tower
Toronto's defining skyline spike, with a glass floor 342 metres up.
The CN Tower is a 553-metre concrete communications tower that dominated the world height record from its completion in 1976 until 2007, and it remains the most recognizable structure in Canada. Built by Canadian National Railway to solve a TV and radio transmission problem, it ended up becoming one of the most visited tourist attractions in the country and a full-blown icon — the kind of thing that tells you immediately, without any other context, that you're looking at Toronto.
Visitors ride high-speed elevators with glass panels in the floor up to the main observation deck at 346 metres, where floor-to-ceiling windows give you a sweeping view across Lake Ontario, the Toronto Islands, and the city grid stretching north as far as you can see on a clear day. There's a glass floor panel — genuinely disorienting to stand on — and an outdoor observation terrace where wind and weather make themselves known. Higher still is the SkyPod, an additional observation level at 447 metres that costs extra but puts you above the clouds on overcast days. The tower also houses 360 Restaurant, a revolving dining room that completes one rotation per 72 minutes and is a legitimate special-occasion spot, not just a tourist trap.
The EdgeWalk, available in warmer months, lets you walk hands-free around the outside of the tower on a 1.5-metre-wide ledge — it's one of the genuinely thrilling urban adventure experiences in North America. For the observation decks, buying tickets online in advance is strongly recommended, especially in summer; queues can be brutal. The tower sits right in the Harbourfront district, steps from Scotiabank Arena and Rogers Centre, making it easy to fold into a broader day in downtown Toronto.