The highest glass floor in the world can be found in Chicago, USA.
The owners of Sears Tower in Chicago have installed four glass box viewing platforms which stick out of the building 103 floors up. As what the they said "The Ledge" is the world's most awesome view, the world's most precipitous view, the view with the most wow in the world. The Ledge is on the 103rd floor. At first they don't feel stepping on the glass floor. But after their 40th trips, they got used to it.
Look at this pictures:

This is Anna Kane. She is five years old. She is looking at the fog at this picture. She may be wondering if she's floating in the clouds. And it seems that its her first trip here. Seems scared here.

But look at Anna Kane now. She was not scared anymore. She lay down on the glass floor and seems comfortable in this picture.
This is Anne Kane with her friend. They seems enjoying now. But OMG! They're looking down the glass door. I can't do that, most especially if its 1,353 feet high! Look at this.

Hello? It's the 103rd floor!
Images from: http://www.worldamazinginformation.com/ and http://www.binscorner.com