There's an old rusty Honda parked in one corner. Piles of twisted rebar, wooden boards and PVC pipes sit near a cart piled with power tools. The massive, hand-built wooden spaceship has a turret seat up top, and the 12-foot-tall lookout platform is reachable only by climbing an extension ladder.

Eight-year-old Simon Pluger paused halfway up the ladder's steps. "Am I supposed to be up here?" he asked.

In this "adventure playground," the answer is yes.

Run by nonprofit Leonardo's Basement, the new outdoor play space in southwest Minneapolis is supervised by adults, but there are only three rules: Be safe, be nice and have fun.

Adventure playgrounds are a far cry from most American playgrounds, which carefully follow federal safety guidelines that ban sharp edges on monkey bars, swings and slides, setting height limits and requiring the ground surface under play equipment to be soft enough to break a fall. Instead, these supervised play areas are loaded with tools and materials with which children can build and destroy. Some even allow kids to literally play with fire.

Long popular in Europe, they're now gaining traction in the United States. The Adventure Playground in Berkeley, Calif. regularly makes top 10 lists of area attractions and the Yard, a 50,000-square-foot play space on New York City's Governors Island, has kept crowds supplied with hammers, nails and saws since 2016.

While some parents may be afraid to turn their children loose in play spaces like this, proponents say they encourage creativity, confidence and self-sufficiency, as kids learn to manage risks on their own.

Every generation has its own ideas about what it means to be a good parent. As millennial moms and dads explore "free-range" parenting and study tips on how to stop hovering, norms are starting to shift away from the once-dominant, anxious, "helicopter" style.

Leonardo's Basement (leonardos basement.org), which has for decades run workshops introducing power tools to kids, started hosting Saturday adventure playground afternoons this summer. Parents register their children in advance, pay $10 and sign a waiver so their kids can play on the structures in the yard, take them apart, add to them or build something completely new using tools and scrap materials like boards, pipes or concrete bricks.

"It feels like what kids way back could do — just run free through the city and just do whatever they want, which you can't really get nowadays," said Minneapolis resident Alyssa Riebe. "It kind of gives them that, but with a little more structure."

That's why Riebe's two kids, Wally, 8, and Eleanor, 6, have been spending plenty of Saturdays at the adventure playground. Although both kids have come home with scraped knees, Riebe said she isn't worried about them getting seriously injured. "That's what it's all about, learning and getting hurt," she said.

Managing the risks

The concept of adventure playgrounds is credited to Danish landscape architect C.T. Sørensen, who wrote about creating playgrounds with "old cars, boxes and timber." The first one opened in Copenhagen in 1943. Minneapolis followed, building one of the nation's first adventure playgrounds. The Yard, as it was called, was funded by McCall's magazine and lured President Harry Truman to pay a visit in 1949.

The playgrounds experienced a surge of popularity in the 1970s, when proponents founded a national group, the American Adventure Play Association. But after parents of kids who were seriously hurt on slides or merry-go-rounds sued parks and equipment-makers, the focus on playgrounds turned to safety.

A 2015 documentary sparked renewed interest in the concept. "The Land," an American film about a Welsh adventure playground, demonstrated how kids were able to manage risks on their own.

Advocates maintain that there's real value in letting children explore limits, instead of trusting that their surroundings have been "made safe" for them by adults.

Leonardo's Basement executive director Steve Jevning believes that traditional playgrounds insult kids' intelligence.

"You take away the creativity. There's nothing you can manipulate. You can't move anything," he said. "It just seems cruel to me."

Even with all of the safety regulations in place, emergency rooms treat more than 200,000 kids under 14 for playground-related injuries every year, according to the U.S. Consumer Product Safety Commission.

Author and educator Gever Tulley, whose TED talk called "5 dangerous things you should let your kids do" has been viewed more than 4 million times, believes safety experts are going about things the wrong way — and that trying to create a bubble-wrapped world that's danger-free is impossible. Kids seek a certain level of adrenaline as they play, and will simply climb up the outside of a "safe" play castle to find it, he said. To Tulley, adventure playgrounds make kids actually pay attention to what they are doing, and help them — and their parents — learn about risk without banning everything that's risky.

"They provide unscripted, intrinsically motivated opportunities for kids to learn how to recognize and mitigate danger," he said. "The great things about these environments is that because they aren't built by adults for the safety of children, kids are having to evaluate everything that they interact with."

The new fort in the woods

Of course, no one is recommending that urban parents encourage their kids to roam through trash-filled vacant lots, even though it may seem strange to pay for your kid to get time in a "junkyard."

"Those impromptu kind of opportunities that you might have if you were in a rural community, where you and I built a fort in the woods or something like that, those just don't crop up," said Tulley. "So you have to create a context where it can happen."

In the yard at Leonardo's Basement on a recent Saturday, one of the most popular structures was a DIY zip line anchored to a junked, parked Honda that one of the nonprofit's staffers used to drive. Wally Riebe stretched a garden hose over to its path and got ready while playmate Jonathan Yaurincela, 7, climbed up, grabbed the handle and leapt, going right through the spray of water.

"That was awesome!" Yaurincela yelled.

Meanwhile, 8-year-old Jack Doty figured out the vehicle was unlocked, and called for his buddies. "Everybody! I'm in the car!" he shouted. Soon, four of them piled in, taking turns vigorously spinning the steering wheel, excitedly messing with the radio and singing along to pretend tunes.

Later, they ran out and asked one of the supervising adults, Chris Groth, for some pieces of wood.

"They found a tray of coins in the car, and now they are building a treasure chest," said Groth. "The trains of thought are so amazing."

Erica Pearson • 612-673-4726

Milo Thompson held tight to the zip line while his friend sprayed him with a hose at the adventure playground at Leonardo's Basement. (The Minnesota Star Tribune)