Chicago is home to one of the tallest buildings in the world: the Willis Tower. So tall that on a windy day, the topmost floors can sway as much as three feet. But what keeps it from falling?

Landmark opened in 1973 with original tenant Sears Roebuck & Co. CHICAGO, Illinois (CNN) -- Sears Tower is history. As of Thursday, the iconic Chicago, Illinois, skyscraper is now named Willis Tower.

An curved arrow pointing right. The Ledge is a glass box on the 103rd floor of the Willis Tower, the eighth-tallest building in the world and the tallest building in the Western hemisphere.

Willis Tower and its Skydeck sit above South Wacker Drive on the western edge of the Loop. You'll find the Quincy/Wells L station nearby, as well as several bus stops and a parking garage.

Then hail follows and lightning strikes the Willis Tower. Warren Buffett keeps taking investors to school as stock meltdown reveals the uncanny wisdom of his recent moves Kurt Russell delights ...

Sunday marked the 32nd Fight for Air Stair Climb, a physically-taxing endurance event that sends athletes of all ages and ability levels up Oakbrook Terrace ... flights at Willis Tower for 16th ...

Chicago is home to one of the tallest buildings in the world: the Willis Tower. So tall that on a windy day, the topmost floors can sway as much as three feet. But what keeps it from falling?