Did anyone catch the "Skywalker" episode?

http://www.channel4.com/programmes/daredevils/episode-guide/series-1/episode-2

Untethered slack lining over 3000ft up. I found it very difficult to watch, but then I'm scared of heights anyway! I just can't get my head around how someone can do something like that? How do you even begin to contemplate crossing a 100ft gap, 3200ft up on a piece of rope an inch wide, without any kind of safety device? Beggars belief!