I love slacklining! We set one up as part of our "home workout area". Great for the core and balance of course, but mostly just super fun. We built some frames and then anchor to a pole on one end and a huge fenced pile of rocks on the other end. You can kind of see the frames in this picture.
The Gibbon slack line package is pretty darn handy, easy to set up, and strong. Great for taking to a park if you don't have trees at home. Sierra Trading Post usually has great deals on them. Gibbon Slacklines Surfline Slackline - 30m - Save 35%