Answer: The world’s first revolving glass floor.
Construction crews recently completed a year-long renovation of the structure, perhaps the most notable part of Seattle’s skyline. The majority of the project involved replacing certain opaque parts of the tower with glass to facilitate unobstructed views of the city. In total, 176 tons of glass were used, 37 of which went to building the world’s first and only revolving glass floor, called The Loupe.
Set on 48 rollers, The Loupe is moved by 12.25-hp motors and makes a complete rotation every 45 minutes. It is composed of 10 separate layers of glass, the bottom four of which are soffit glass, so they are see-through from above but opaque from below. The bottom layers also are stationary and do not rotate along with the other six.