A giant zip wire (other wise known as a Tyrolean Crossing or Flying Fox to those Down Under), is basically a daddy version of the old kids 'Death Slide' on steroids. There are a couple of versions to the theme, the most common being a simple high speed traverse over a valley or gorge harnessed to the wire. The variations to the theme come into play when there is a member of the party who is 'celebrating a special occasion'. It is often part of the course to get the lucky chappy to run the gauntlet in their birthday suit and (depending on the location and spunkiness of the boy/girl of honor), rise to the challenge of avoiding a hail of paintballs volleyed from their compatriots in true Jackass style.

Another version on the theme (little less humiliating), is the Tyrolean Drop, which is pretty much the same as previous, except you become 'unhooked' half way through your decent and drop from the wire into a river running below.

Note
The Zip Wire is great fun but really needs to be combined with at least one other activity to make a multiactivity day.