Slacklining is an *extreme-nut* sport of balance. It is a version of "tightrope walking" across great heights (note: distinct difference from tightrope: the rope is not as taut, but more elastic, trampoline-like).
Christian Schou currently holds the Guinness World Record title for the highest slackline (or tightrope walk). He accomplished this feat in Kjerag, Norway at 3,280 feet or 1000 meters (that is 3 times the height of the Eiffel towers!).
The painful to watch video is unfortunately not in English. Skip ahead to 2:19 for his insanely-close-to-death balancing act:
Death seems like a true possibility...but if you consider yourself a dare devil, scroll all the way down for the beginner's guide.