Slacklining is usually done between two trees, not high off the ground. But this past December, a group of daredevils took a slackline high in the air to form a tightrope between two cliffs in Sidney, Australia. Slacklining at a significant height is called highlining.

Photographer Cameron Spencer snapped photos of Kyle Beall, Luke Sarantos, Matt Macelli and Antek Marciniec crossing Diamond Bay by slackline, with the thundering ocean visible below.

Of course, the extreme sportsmen are secured to the slackline with a harness. Falls do happen, and Spencer captured a few missteps, as well as the slackliners using their core strength to get back into position on the highline. View the slideshow above for the incredible photos.

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