Through the glass observation panels in the floor, I looked down at the sea, nine hundred feet below us.

NPR: Excerpt: 'Skybreaker'

Mr. Coffey has worked alongside cleaning machines at times but said his most important jobs, including cleaning the glass observation deck at the Twin Towers, have always been done by human hands.

WSJ: Window-Washing Robots Rise; Humans Balk

The evidence discovered was remarkably detailed: the plotters appeared to have been putting the targeted buildings under close observation, gathering such details as the thickness of the glass in their windows and the numbers of security guards on duty at various times.

ECONOMIST: America and Britain on guard | The

Ride a glass elevator to the 160-meter-high observation deck for an incredible view of the city and its surroundings.

CNN: Seattle: What to see