A zipline is a cable stretched between two points at different heights, usually with the higher point at the top of a hill, tower, or platform. To ride a zipline, you clip a pulley and harness to the cable, then gravity pulls you down along the wire, often at thrilling speeds. You might zoom across a valley, over a river, or through a forest canopy, with the wind rushing past your face.

Originally, ziplines were practical tools used in mountainous regions to transport supplies or people across canyons and rivers. Today, they're popular attractions at adventure parks and vacation spots, though some researchers still use them to study rainforest canopies without disturbing the trees.

A zipline needs enough slope to keep you moving. Too flat, and you might get stuck halfway across. Too steep, and you'll arrive at the bottom platform way too fast. Good zipline operators carefully calculate the angle, cable tension, and braking system to make the ride exciting and safe.