Highlining is essentially the same thing as slacklining, just at ridiculous heights. What they do is anchor a rope between two points and then walk across it. Let me break down the 3 Types of Highliners:

Level 1: Circus-Wannabe-Guy
Highlining at survivable heights with a security rope, which looks like this:

“I highline better in black jeans.”

Level 2: Rock-Climing-Isn’t-Extreme-Enough-But-I-Love-Mountain-Dew-Guy
Slightly crazier guy that kicks it up a few notches on the Extreme Scale and does it in the mountains, with a security rope:

“If I fall or run into any bad guys, Sly Stallone will come save me.” [photo credit]

Level 3: Ballsier-Than-You’ll-Ever-Be-Guy
This nut’s name is Dean Potter and he put up his line in between some mountain rocks at Yosemite National Park. Oh yeah, he’s got no security line or safety net. Watch the video:

So he got across one way, but wouldn’t that suck if he fell on the way back? How does he get to safety?

Thanks Kyle.