I saw this video posted on a few different websites & it's not for the acrophobic.
Just watching this made my palms sweat & my heart rate go up! Let's just say I wouldn't volunteer to be 1000's of feet in the air w/ no stable surface beneath me.
This kind of work is a modern equivalent of the construction workers on the girders in old photographs.
Toward the end when he says "This is the tricky part," @ 6:45 is definitely an understatement.