My parents gave me a slackline for Christmas, so we rigged it up between a tree and Dad's 4WD to try it out. To begin with we had the line about 10m long but the wind was bouncing it around and making it extremely difficult so we backed the car up a bit and shortened the line to 5m. This made the line much firmer and easier to balance on (still tricky!). Spent the afternoon playing around and gradually improving.
A fun way to work on core strength and balance!