B.C. slackliner breaks world record by balancing unharnessed between cliffs

Imagine this: You're walking across a line -- almost 300 metres in the air -- and you don't have a safety harness on.

Well, that was a reality for daredevil Spencer Seabrooke when he appeared to break the world record for free soloing a slackline earlier this month.  

"It's all been building up to this," he tells As it Happens guest host Peter Armstrong.

Seabrooke picked up slacklining three years ago. This, however, was his biggest walk to date. It has not yet been officially declared a record.

In a newly-released video of the stunt, Seabrooke crosses a 64-metre gully at British Columbia's Stawamus Chief Mountain. The line is suspended around 300 metres above the ground. Seabrooke is not wearing a safety harness.

"It would take about seven seconds before you hit the ground," he says.

For those not familiar with the sport, Seabrooke says slacklining is very similar to tightrope walking - but with one crucial difference. "It's not on a rigid cable. It's on a very flexible and dynamic piece of flat webbing."

It is traditionally practiced a few metres from the ground. What Seabrooke does -- called highlining -- is less common.

"A lot of people don't have the guts for it," he says.

Seabrooke has been preparing for this stunt since August of last year.

"I had done many laps wearing a harness and full safety gear," he says. "I've probably crossed it -- with no falls -- close to 30 times."

But, this was his first time doing the walk without a harness.

"The most difficult part of the whole walk is when you stand up and you have the entire line out in front of you. Any little movement that I make gets multiplied throughout the line."

For Seabrooke, the key to his success was mental preparedness.

"You can't have a doubt in your mind before you start something like this because that doubt will eat away at you when you're out there."