Here's one case where I'd say go ahead and try this at home -- like a foot above your soft mattress. As for what this guy's doing...

Yesterday's Marin Independent Journal explains:

What looks like a publicity stunt for Barnum & Bailey tightrope walkers is actually a sport known as "slacklining" or "highlining," in which daring participants walk on a 1-inch-wide strand of nylon webbing — a slack line — sometimes suspended at dizzying heights above the ground and often in areas of great natural beauty...

While the activity appears dangerous, [21-year-old Randy] Thompson said a lot of thought goes into safety for the participants.

"We use safety equipment although some people do what's called 'free soloing' where they don't use safety gear," Thompson said. "People work very hard to make sure it is safe. There are a lot of redundancies with the rigs for safety. It's a very planned-out process."

But it's generally not planned out to a point where local land managers are notified when the lines go up, acknowledged Andy Lewis, 25, a Redwood High School graduate who is a well-known figure in the sport.

And from the potential killjoys:

Golden Gate National Recreation Area spokeswoman Alex Picavet said law enforcement has taken a live and let live approach.

"As long as there is no resource damage and they are not endangering anyone and they take their equipment with them, then it's legal for them to do it," she said.

Marin Municipal Water District watershed manager Mike Swezy — who helps oversee activities on Mount Tamalpais — said the activity happens too infrequently to have a policy against it, but that rangers would attempt to deter highlining if they saw it.

More on the guy in the video, Andy Lewis, here:

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Video: "Slackliner" Andy Lewis Walks High Above Marin Headlands