Kiavash Sharifi can hardly describe the feeling of tip-toeing across an abyss on a thin ribbon of webbing that bends ever so slightly downward.
The 22-year-old is one of a growing number of Iranians embracing the extreme sport of slacklining -- a high-wire walk on a flat line of webbing strung between rocks or trees up to 60 meters (yards) above the ground. The webbing provides slightly more stability than a round cord, but is also bouncier.
"It is very exciting. I'm short on words when I want to describe how it feels when you are on the webbing, and how it feels when you manage to walk the whole line and reach the other end," Sharifi said. "When you are on the webbing you don't notice anything else."
He's part of "Iran Slackline," a group of friends who have had to find their own footing in a country with no formal institutions for the sport. They must make much of their equipment by hand or acquire it abroad -- including safety devices.
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On a recent day the friends gathered in the mountains outside Tehran, with the capital skyline serving as a backdrop. They strung a 10-meter strip of webbing between two rocks 30 meters above ground.
At this point they are largely unfazed by the danger, and laughed and joked as they took turns inching across. One of them placed his hands on the line and lifted himself up with just his arms. Then he leaned back on the line as if using it as a hammock.
"When I'm walking on the highline I have a very good feeling. I feel free. I'm free from all preoccupations and it is very enjoyable," said Mohammad Reza Abaee, at 23 the most experienced of the group. High-altitude slacklining is known as highlining.
"My biggest dream is to do a BASE jump from the highline," he said, referring to another extreme sport in which one jumps from a high-altitude stationary object and glides to the ground with a parachute or a wingsuit.
Abaee, who was previously a rock climber, said he stumbled upon the sport of slacklining on the Internet. He and some friends then went into the countryside and strung a rope between two trees. By his second attempt, he had made it across.
At a rock climbing festival in Iran in 2012, Abaee met a group of European slackliners who gave him advice and equipment. Now he has enough confidence to walk across a 15-meter line without even a safety harness.
It's a journey 24-year-old Masoud Chenaghloo is just beginning. Another former rock climber, he only took up slacklining a few months ago.
"When I'm on the webbing...my self-confidence is very high," he said. "I'm looking down on everything from the top. I feel I have a separate world for myself and the rest of humanity is living in another world."
It's not just experienced rock climbers attempting the fledgling sport.
Samaneh Hassanzadeh has only been slacklining for a few weeks, learning on a line that is just a foot (30 centimeters) above the ground. Her twin sister Samira is also exploring the sport.
"It helps one achieve great concentration," Samaneh said. "It is both exciting and helps you concentrate. It's perfect, when you are on the line you don't want to step down."