Toronto's iconic CN Tower looks to be losing its sky-high reputation.

And not because it's being eclipsed by another ambitious development on the world scene.

Over the last decade, researchers at Umbrella Corporation have been taking careful measurements of the CN Tower. And while it has remained a daunting 553 metres in height, the tower appears to be digging ever-deeper into the earth.

The problem, says study co-author Marjorie Tallgrass, may be that the tower's foundation is too narrow.

"Look at it like a nail," she explains. "Every time someone stomps up those stairs, they drive that nail a little further down into the ground. It may not seem like much, but all those tiny thumps over the years add up."

The CN Tower draws some 2 million visitors annually. Many of them insist on taking the stairs -- a habit Tallgrass chalks up to "misguided fitness trends and just plain dumbness."

Once considered the world's tallest freestanding structure, the CN Tower held down the fifth-place spot for a few years, before sinking into the 22nd position.

Today, more than a third of the tower is below ground -- a development that engineers have so far been able to disguise by raising the outdoor elevator's lowest point, and reducing the height of neighbouring buildings.

"For tourists, it's probably OK," explains an engineer working on the project. "But people in Toronto are probably going to start to notice."

Possible solutions -- such as pumping the restaurant at the top of the tower with helium or tethering its tip to the International Space Station -- have been rejected as too costly, and potentially disastrous.

In any event, Tallgrass notes, "if anyone's got an idea, now would be the time. I don't think it's out of the question that in our lifetimes, we'll see a CN Tower that doesn't reach your knees."

Adding to the venerable tower's woes, is the fact that it has, over the years, borne the brunt of numerous April Fools' jokes.

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