If you think your balance is good, check this out (has a bit of a long intro though)....
When I used to be a rock climbing bum we used to do this in the camp ground just to have some fun... When I said we used to do this... I was super happy to just stand up without falling and having the slackline smack me in the nuts!
Yeah slacklines (and tightlines) can be fun but for a bit more excitement how about some highlines 
