The second-tallest building in the Western Hemisphere (the tallest if you’re not counting antennas) provides an unrivaled view of a cityscape, all from the comfort of four glass platforms suspended 1,353 feet in the air. Located on the Willis Tower’s 103rd floor Skydeck, the observation perches have walls, floors, and ceilings made entirely of glass, allowing visitors to jut out from the edge of the building to enjoy a unique and vertigo-worthy view of Chicago’s architectural landscape.

Though the building is now officially known as the Willis Tower after being acquired in 2009, it’s still commonly referred to by its former name, the Sears Tower. It’s the 14th-tallest building in the world with 110 stories constituting 1,450 feet. The glass cubes, called “the Ledges,” were opened to the public in 2009. Each of the four compartments measure ten feet by ten feet and protrude 4.3 feet from the edge of the tower.

With three layers of glass totaling one-and-a-half inches thick, each platform can support up to five tons. A completely transparent three sides, top, and bottom designed to generate the sensation of hovering over Chicago do just that, as the boxes are wide enough for one row of visitors to stand suspended at a time. A clear day presents a view of up to 50 miles and four states.

Structural glass design experts Halcrow Yolles took the original architectural plans of Skidmore, Owings & Merrill a step further, from the concept of a retractable structure for easy cleaning to a glass box with near-invisible structural support. All the side and bottom perimeter steel was removed, completing the floating-on-air appearance.

The idea for the Ledges supposedly originated from the constant cleaning workers had to do on Skydeck’s windows. Every day, tourists would press their foreheads against the glass, attempting to peer down at the city, leaving smudges that were becoming tedious to clean. Now, all the staff need to clean are the occasional footprints left by fearless children, or the handprints from nervous adults ensuring themselves that the walls are still there.