One of Canada’s national treasures and Toronto’s very own landmark -- the CN Tower -- is celebrating the big 4-0 today.

According to Canada Lands Company -- a Crown corporation that manages real estate, development and attractions -- the CN Tower held the title of the world’s tallest free-standing structure when it was built in 1976. Though later outdone by the Burj Khalifa in Dubai, the tower remains the tallest in the Western Hemisphere and its “EdgeWalk” tour currently holds the record as the world’s highest outdoor walk.

Its assembly required more than 1,500 construction workers, 40 months of around-the-clock work and $63 million to build, a fact sheet by the World Federation of Great Towers states.

By 1995, the tower was named one of the Seven Wonders of the Modern World by the American Society of Civil Engineers, sharing the title with other famed landmarks such as the Empire State Building and the Golden Gate Bridge.

But the CN Tower is more than just a picture perfect postcard– it also works as a communications tower by providing transmissions for a number of different TV and FM radio stations.

Today, the CN Tower is a beacon for events, memorials and celebrations, and a key destination for newcomers to Toronto. It’s ability to light up in different colour patterns – including a rainbow colour scheme to honour the upcoming Toronto Pride parade – makes it an ever-changing part of the Toronto skyline.

In honour of the tower’s 40th birthday, people are taking to Twitter to share memories, photos and happy birthday wishes to the Toronto favourite.