The Willis Tower is at its best when you're dangled over one of its glass-bottomed balconies 396 metres above Chicago.

For the city that invented the skyscraper, size against the skyline has always mattered to Chicagoans. So the Willis Tower holds a special place in their affections, ever since it seized the 'tallest building in the world' title way back in 1973, when its antennae scraped over the 518-metre mark. Others may have acquired the title since, but the Willis Tower remains the tallest building in Chicago, and the US – as well as one of its most recognisable. The lazy steps it takes, to get up to its highest point, suggest a breezy casualness towards its epic size – which goes down well with the citizens of the Windy City.

But the thing that matters most to the visitor – apart from the fact that the Willis Tower is always there, no matter where you are in Chicago – is that this is a tower built to be climbed and viewed from. It has a purpose-built deck, the Skydeck, which sits almost at the top, on its 103rd floor. That's an eye-watering 412 metres above the busy city streets – high enough to make your ears pop, on the way up in the lift. The Skydeck opened at the same time as the building – in 1974 – and has since undergone a dramatic upgrade.

The Willis Tower itself has had a few dramas along the way, too. It was built in the heyday of the Sears Company, when it was one of the biggest retailers in the US. But it lost ground in the 1980s, and the Sears Tower was never fully occupied. Sears abandoned it in 1992, leaving it without an official name. Then, in 2009, the Willis Insurance Group took up some office space, and bought the name. But if you ask any self-respecting Chicagoan, it remains the Sears Tower to this day.

Whatever you call it, you can't argue with the view from the Skydeck. On a clear day you can see across the 161 kilometres of lake to Michigan State in the east, and take in large tracts of Wisconsin and Indiana to the north and south. And the newly-installed 'Ledge' has glass-bottomed balconies extending several metres out from the Tower. If you dare to step onto them, you'll have the peculiar feeling of floating over a Windy City, which becomes almost toy-like in appearance. Only the Willis Tower can do that.