Early one spring morning several years ago, I received an email from my USSR-born, New York City-bred, theater-director friend Yelena inviting me and my family (which then consisted of my husband, Frank, and our two sons, King and Mick, ages five and two) to visit her and her family (which then consisted of her husband, R, and their two sons, Chuck and Gen, ages four and one) at their new home in Tokyo, with the understanding that if we chose to come, we would stay for at least a month.

I do not believe the English language contains a word that expresses all this gesture was. Her invitation to us was a feat. She inhabited her space with such generosity that she enlarged it. And then, from that expanse, she called to us: Come in.

When we got the invitation, my husband, Frank, and I looked at each other: When would we ever have an opportunity like this again? We told the boys we were going on a journey to Japan. I pointed out New York on the globe.

“From here,” I said, dragging my finger across the world as I simultaneously spun it, “to there.”

They glanced at us, unfazed, and continued pushing their smiling toy trains around the figure eight of wooden track that was set up on the train table.

* * *

Yelena waited about a week before she took us to the place that I believe had been her goal from the beginning. She wouldn’t tell us anything about it except that it was a playground; she hoped we liked it; not many foreigners knew about it; and she and Chuck had a nickname for it: Savage Park.

Just as the Diana Ross Playground is located in the larger Central Park, Savage Park, also known as Hanegi Playpark, is located in a larger park called Hanegi Koen. It took us a while to get to Savage Park because we had to walk past several other playgrounds within Hanegi Koen, and given that half our ranks were age five or less, we could not easily walk past a playground. As the eight of us walked, first up a slight dirt hill, then past a gaggle of unlocked bicycles, we smelled it: smoke.

The smell became stronger as we went ahead. We followed it until at last we were all standing beside a traditional Japanese hut that was perched atop a downward-sloping one-acre patch of dirt and trees.

The hut’s front porch was completely overflowing with crap, including a pink-painted piano at which a girl, five, was sitting and playing a John Cage-ian ditty. It was a strangely radiant sound to be hearing as we stood there looking down through the smoke—we could see it as well as smell it now—to the smoke’s source: open fires.

There were three of them. At one, a boy about eight years old was kneeling, poking at the flames with paper fans; at another, a father was sitting and roasting marshmallows with his toddler son. A third fire seemed to be unattended.

Frank and I turned to look at Yelena, who had stepped to one side and was smiling twinklingly at us.

We stood there, dumbfounded, staring at the dirt and trees and the structures that were woven around and between them, structures that were clearly not made in any place where safety surfacing had ever been a subject of serious discussion. These were structures that looked like what remained when my sons decided to build an airport out of Legos and then abandoned the project halfway through, only these half-made baggage carts and control towers were much larger and crafted not from nicely interlocking plastic rectangles but from scraps of wood and nails.

This was possible because (as our boys would soon discover), the materials to make the structures—hammers, wood, saws, hole punchers, screwdrivers, nails, paint, brushes, and donated scraps of all kinds—were available at the playpark for everyone to use. The boys took off running. Frank and I stumbled after our children. The ground was uneven; the park did not seem to be landscaped in any recognizable way. There was dirt underfoot, one presumed, because grass could not possibly survive the trampling; likewise, there were trees around the area because that’s where they grew.

At one point, I looked up at the trees. I was astonished to see that there were children in them. The more I looked, the more children I saw. There were children 15 feet high in the air. There were children perched on tiny homemade wooden platforms, like circus ladies dressed in glittery clothes about to swan-dive into little buckets. There were children sitting up there, relaxed, in their navy blue sailor-type school uniforms, chatting and eating candy on bitty rectangles of rickety wood as if they were lounging on the Lido deck of The Love Boat. There were children, preteens, crouching 15 feet up on the roof of the playpark hut and then—I gasped to see this—leaping off it onto a pile of ancient mattresses.

King and I sat on a log, eating warm, white gooey marshmallows. The park was around us, and the trees were around us, and the dirt was around us, and the smoke, and the music. The children were in the trees, and were flying in the air.

We stayed there as long as we could.

* * *

A very good resource for someone who is interested in going to a playpark and picking up a hammer and nails and pounding away at scraps of crap to make something is the work of the 19th-century British writer John Ruskin. In Ruskin’s On Art and Life, a contemporary repackaging of two of his essays, “The Nature of Gothic” and “The Work of Iron, in Nature, Art, and Policy,” he offers a moving plea for allowing men—in particular, the men who built the Gothic cathedrals of the age—to be, as he says, “fully men” and not mere tools of the architect; to be allowed to use their imaginations in their work, to be allowed to make mistakes.

Let him but begin to imagine, to think, to try and do anything worth doing; and the engine-turned precision is lost at once. Out come all his roughness, all his dullness, all his incapability; shame upon shame, failure upon failure, pause after pause: But out comes the whole majesty of him also; and we know the height of it only when we see the clouds settling upon him. And whether the clouds be bright or dark, there will be transfiguration behind and within them.

In this, written more than a 150 years ago, he articulated why my modern-day love of Savage Park was so immediate. It wasn’t just that the children were flying in the air there, it wasn’t just that they were making insanely great structures, it wasn’t just that the playpark hut was a junk lover’s dream. It was because the place existed at all for just this reason: the full and complete allowance of a self, including all the ineptness, failure, and possibility of death—because it is understood that only with this allowance do we have the capacity to be great.

Savage Park was not a new and exotic topography, and Ruskin, in his way, mapped this landscape more than a century earlier when he listed the six characteristics of Gothic architecture: The first, above all others—above changefulness, naturalism, grotesqueness, rigidity, and redundancy—was savageness.

* * *

According to Hitoshi Shimamura, the International Play Association regional vice president in East Asia, the pilot park that became Hanegi Playpark was founded in 1975 on a one-acre plot of land formerly used as a dump. It was modeled on the first adventure playground, which was created by landscape architect Carl Theodor Sørensen and which opened in Emdrup, Copenhagen, in 1943, when that town was under German occupation.

According to play researcher Susan Solomon’s book American Playgrounds: Revitalizing Community Space, this first-ever adventure playground had, essentially, three components: a vacant lot; donated scraps; and a single adult supervisor, who “was available only for guidance and was key to the success of the playground.”

Sørensen’s playground, then known as a “junk playground,” was the seed for many more. According to adventure-playground advocate Lia Sutton, there are currently about a thousand adventure playgrounds in Europe, largely in Denmark, Switzerland, France, Germany, the Netherlands, and England.

Adventure playgrounds arrived in Britain in the 1950s, where they benefited greatly from a powerfully placed playground advocate, trained horticulturist Lady Allen of Hurtwood. As a result of her zeal, many adventure playgrounds were set up in the British Isles. In the United States, adventure playgrounds simply did not take hold in the same way.

Playgrounds themselves emerged in the United States in the 1880s, when, as noted by Howard Chudacoff in his book Children at Play: An American History, the playground movement in the United States began, and “reformers established sand gardens in parks and schoolyards to promote play among very young children.”

In the early 1900s, the Playground Association of America was founded, and that event marked “the professionalization of playground work.” By 1917, the country had 3,940 public and private playgrounds, and it employed 8,768 playground directors.

With the advent of the automobile, the playground served a basic need: It got the children off the streets and out of the way of vehicles. In 1922, automobiles caused the death of an astonishing 477 children in New York City. But during the Depression, playground funding was cut, and the movement sputtered.

The economy improved following World War II, but the public playground’s decline continued, because middle-class families provided their children “with their own play accoutrements at home,” as Chudacoff noted, and backyard playgrounds competed with public play areas.

In the 1950s, the playground in America began a brief relationship with the art world, because, as Solomon wrote, the connection “between playgrounds and sculpture began to take hold.” In 1954, the Museum of Modern Art held a playground-design competition that received significant media attention and heightened the legitimacy of playgrounds in art circles and elsewhere. The association between playgrounds and art did not last long; safety issues became important, and commercial products filled the playparks. Lady Allen of Hurtwood toured American playgrounds in 1965 and called them “an administrator’s heaven and a child’s hell.”

In the 1970s, with the emergence of an energetic new do-it-yourself movement, homemade play spaces became more compelling. Jeremy Joan Hewes’s inspired and inspiring 1975 book Build Your Own Playground! focused on the West Coast designs of Jay Beckwith, who incorporated many of the adventure-playground ideas in his instructions for making tunnels and ramps out of rope and discarded materials. It was on the West Coast during that period that one of America’s few, still operating, year-round adventure playgrounds was founded: the Berkeley Marina Adventure Playground.

The Berkeley playground opened in 1979, around the same time as Hanegi Playpark, but it is structured somewhat differently than its Japanese counterpart. Whereas Hanegi Playpark is for all ages, Berkeley is meant primarily for children seven and older; younger children are welcome as long as they are kept “within arm’s reach” of an accompanying adult, administrators state on the playground’s website (italics theirs). Also, every child who enters the Berkeley playground must have his parent or guardian sign a waiver releasing the playground from liability for any injuries that might occur there.

The Berkeley playground website tries to prepare parents for the many hurdles they will face when they bring their children to the park; its guidelines remind parents to keep their cell phones in their pockets and use good judgment. “If what they are doing is destructive and dangerous,” the website advises, “please stop them and clean up.”

In contrast, Hanegi Playpark’s primary advice consists of a sign posted near one playground entrance that reads: Play freely at your own risk.

This article has been adapted from Amy Fusselman's Savage Park: A Meditation On Play, Space, and Risk for Americans Who Are Nervous, Distracted, and Afraid to Die.