How does a zip-line work?

Easy: It's a very basic principle, you ride on an aircraft grade steel cable using a pulley and a safety harness with a main safety strap wich can carry over 20 times your own weight and a second one acting as a backup. You displace using gravity because the cable has a slight tilt downwards, this makes the cables unidirectional which means they only work one-way and not back. You may now wonder about the brakes, well, your pulley has a friction brake which stops you at the end of the zipline and there is always an instructor waiting at the end to assist you. This simplicity is what makes it so safe. Nothing too complicated which makes it impossible to have any user error.