A tourist activity in a forest (ideally, a rainforest, such as Costa Rica's Cloud Forest).

The idea is simple: wires are strung between trees at an angle, just below the treetop canopy (typically 50 to 100 feet above the ground), with small platforms to stand on where the wires meet the tree. The tourist is strapped into a safety harness, and somehow gets to the beginning of the top wire; methods for doing this include climbing a ladder or rope, or hoisting the tourist by means of a rope and pulley (some operators force the tourist to hoist themselves). Once at the top platform, the harness is attached to the wire, and the tourist whizzes down the wire -- again, usually 50 to 100 feet above the ground -- to the next platform, using a gloved hand to grip the wire and brake when necessary. Once on a platform again, the tourist gets switched over to a new wire, and the whole thing repeats.

As in any activity where your life depends upon the safety gear provided by the operator, fly-by-night operators should be avoided like the plague; setup costs are cheap, so it is vital to ensure that your chosen provider has a good safety record. However, views from just underneath the treetop canopy are amazing.