October 2011, Esplanade Park, Boston, Massachusetts. A light wind ruffles the red, brown and yellow leaves as the deep, slow Charles River bends its way around the park. A lone, slender figure methodically walks over tensioned webbing slung between red oak and white willow trees. The 200-foot tensioned line bobs and weaves under her weight, and, when she reaches the center of it, her bare feet scrape the tips of the grass.

Concrete and steel high-rises, signs of Boston’s busy metropolis, poke into the sky in the distance. But the lone figure, Sonya Iverson, barely notices any of it. She’s in her isolated world, focusing on putting one foot in front of the other without losing her balance and getting bucked from the line.

She fights the urge to tense up—if she does, she’s off. Instead, she focuses on the moment, keeping her mind and body relaxed, working under the power of muscle memory. The walk acts as moving meditation. Slacklining takes her away from her studies in molecular biology and earning her Ph.D. at Boston University, calming her and resetting her for the upcoming week of intensive work.

When she steps off, she sees a few curious onlookers are standing near the line, startling her back to reality. The 20-something Millennials (like her) are hoping to get the chance to try out the sport. She goes over the basics with them, one by one on the line: Keep your body upright like a tree. Look straight ahead to keep a good center of balance. Walk carefully.

The following weekend she returns to Esplanade Park, this time with an extra line, a short one no more than 30 feet long, for first-timers—should they arrive—to play on while she works out the moves on the 200-footer. (The longer the line, the harder the challenge.)

Soon a crowd 30 deep begins to assemble in front of the beginner line. The word is out.

Online Community

Nine years ago, while living in Bozeman, Montana, Iverson picked up slacklining, learning  by trial and error with her boyfriend at a local park. For months, they set up and broke down the line using carabiners and knots, starting with 30 feet and working up to 90-foot spans.

Sometimes the line was too tight, other times too loose. And there were falls—missteps, where trained reflexes allowed her to hop off the line before slamming into the grass. Other times, the line would spring back and smack her in the back of the legs.

Finally, after weeks of time-consuming progress, they saw highliner Josh Simpfenderfer setting up a massive 280-foot line. Watching in awe from across the park as he danced across, they sidled over. Soon he was offering advanced slacklining tips to her. Iverson absorbed every word, and she and Simpfenderfer became fast friends. A few weeks later, he showed her the art of highlining—walking lines rigged hundreds or thousands of feet above the ground.

Without his mentorship and safety tips, she may have never graduated to highlining.

But three years later, in 2011, with the group of Bostonites surrounding her at Esplanade Park, she got the chance to pay Simpfenderfer’s generosity forward. Instead of continuing to teach the group of eager slackliners one-on-one (there were too many), she started a community Facebook group, Slackline Boston, where “slackers” could learn about rigging lines and meet-ups with fellow members. Within a few years, Slackline Boston became one of the biggest slackline groups in the U.S., with 795 members currently on its Facebook page. For her part, Iverson was hooked on spreading the word.

So she started the non-profit Slackline U.S., modeled after the climbing advocacy organization the Access Fund, to provide safety and access information to the community. Next came the community forum Slack Chat, which connects practicioners of the sport and gives them a place to talk about community, problems and technique.

Seven years later, through building slacklining websites and acting as moderator—and reaching out to city officials when slackers got busted for walking their lines, say, in Colorado and Oregon—she’s become the de facto spokesperson for slacklining in the U.S. “Boulder is a great example of successfully working with the city,” she says.

Now, in addition to maintaining her sites, Iverson slacklines 100 days a year. She’s also walked lines as high as 1,000 meters (3,281 feet) and attempted lines as long as 220 meters. She’s traveled to 15 countries, including Iran and Turkey, to teach and perform on lines.

To practice her sport and travel, she lives a nomadic lifestyle out of her maroon 2002 Pontiac Grand Prix. “I don’t often sleep in my car, but I live out of it,” she says. “My home bases are Montana, the Bay Area (California), Copenhagen, Denmark.”

Iverson says there are three issues slackers run into in city parks: concern for the safety of the trees, liability and a general “‘We don’t know what slacklining’ is mentality which is what I call the skateboarder syndrome,” she says. “People didn’t understand skateboarding in the mid-‘80s, and when you don’t understand something, it’s easiest to say ‘you can’t do that here.’”

Boulder Booming

In spring 2016, Tyler Shalvarjian and his friends were slacklining in Boulder Colorado’s Martin Park when they were fined $250 for attaching an object to trees, an antiquated law intended to prevent horse tethers from damaging bark. They were cited under “Boulder City Code Section 6-6-6(c), ‘Protection of Tree and Plants,’ which prohibits attaching anything to a tree on city-owned property,” (BoulderColorado.gov).

The group contacted Slackline U.S. for help. “People had been kicked out of Martin Park before. This was the first time there was a ticket,” says Iverson.

She worked with a group of Boulder slackliners led by locals Ken Wagers and Katie Frayler to prepare their approach before getting in touch with the city’s Parks and Recreation office for a resolution. They aimed to open communication and provide documentation on the sport of slacklining, the legality behind it, and what worked managing it in other areas.

By winter, Boulder officially recognized slacklining and released their rules and regulations guide for slackline access on public lands. On its website the city stated: “In 2016, Parks and Recreation staff worked closely with a community group of slackliners to explore ways to attach the slackline in a manner that doesn’t harm the tree and agree on specific trees that are suitable for the sport. By working with the community and exploring rules and protocol from other peer communities, the city developed and proposed a rule change to allow safe slacklining in designated park locations while protecting trees.”

Rules state that lines can be no higher than four feet off the ground at the center when weighted; lines can only be set up and used during daylight hours, and must be removed daily; trees must be protected from harm; and flags have to mark lines greater than 50 feet in length. The city also posted an interactive map on their website showing trees designated for slacklining. Open areas include Melody Park, Howard Heuston Park, Scott Carpenter Park, Beach Park, Admiral Arleigh A. Burke Park, Martin Park and Bear Creek Park.

“The Boulder rules are the best of any towns with regulations,” Iverson says. “Now we’re using this as a model for opening up access in other places where slacklining is not allowed. The more cities where slacklining is legalized with reasonable regulations like this, the easier each new conflict resolution becomes.”

Slacklining is now the future.

EO Contributing Editor Chris Van Leuven’s work has been featured in Best American Sports Writing 2016.