Not for those who fear heights.
This month itself (Aug 2015) Spencer Seabrooke took to the mountains to break the longest free solo slackline World record. Seabrooke was suspended 290 meters in the air and walked 64 meters between two cliffs.
The beginning is terrifying, as he falls and catches the rope multiple times, saving him from falling to his death. Once he gets into a flow, he traverses the line with ease.