There's usually a slide, a bridge, and a high point with a domed roof.

That's what makes this a playground, and this, and this.

But what about this?

This isn't a junkyard.

It's called an adventure playground.

Here, there are no plastic play structures, just things like old tires, wood planks, and hammers and nails.

Places like this represent one of the most debated ideas in play architecture : that playgrounds should be designed to let kids take more risks.

Now, this nightmare for helicopter parents is the hottest new thing in American playgrounds, because there's growing evidence that play like this is a whole lot healthier, and safer, for kids.

"They can play with very dangerous tools, they can take really dangerous risks and overcome them."

"And this builds up a tremendous sense of self confidence in themselves, which is really quite fascinating to watch."

That's Marjory Allen.

She was a British landscape architect and children's welfare advocate around the middle of the century.

In 1945, she visited Copenhagen, where she met an architect named Carl Theodor Sorensen.

Two years earlier, during the German occupation of Denmark, Sorensen noticed a problem: kids in his neighborhood weren't using playgrounds. In fact, they were playing just about everywhere else, even in construction sites and bombed-out buildings.

So, in a housing development in the suburbs of Copenhagen, Sorensen closed off an empty lot and filled it with building materials, discarded objects, and tools.

Here, kids could dig, and build, and invent on their own.

The play structures were ultimately designed by the kids themselves.

Sorensen called it a junk playground, and kids and parents loved it.

When she returned to England, Marjory Allen started opening similar playgrounds all across London.

And she renamed them: from junk to adventure.

From there, they became a global phenomenon.

They spread to Minneapolis, Boston, Toronto, Tokyo, Houston, Berkeley, Berlin.

And to create these playgrounds, designers had to introduce a critical element: controlled risk.

In this context, a risk isn't the same thing as a hazard.

When you're climbing a tall tree, a rotten branch is a hazard: the threat is unexpected.

But how high you climb is a risk: it's manageable, and requires you to actively make a decision.

You can break the elements of controlled risk down into 6 categories: heights, speed, tools, dangerous elements, rough and tumble play, and the ability to disappear or become lost.

And a good adventure playground includes a mix of these.

Designers also focus on separation of space.

To give kids the feeling of discovering things on their own, parents have to stay out.

That can mean installing a physical barrier or providing things like restrooms, cafés, and seating, so that parental experience isn't an afterthought. Finally, designers fill it with loose parts.

These are the manipulatable objects, the planks, barrels, bricks, and tools, that fuel risky play.

The idea behind all these design elements is that kids respond well to being treated seriously.

If they're presented with risky items with a serious functional purpose, they'll respond cautiously and conduct more experimentation.

But if presented with an overly safe, static space, they often wind up seeking dangerous thrills that the built environment fails to provide, which can result in higher injury rates than risky play at adventure playgrounds.

In the US, a culture of lawsuit-proof playscape design means that overly safe playgrounds are the norm.

And design philosophy has focused on how to reduce height, movement, and hard materials.

And that hasn't made playgrounds better.

When Marjory Allen visited American playgrounds in 1965, she called them "an administrator's heaven and a child's hell".

But adventure playgrounds have recently begun to catch on in the US, perhaps due to an effort to introduce more unstructured play.

And their construction comes with a fair share of criticism.

"They're making kids play with hammers and nails. That's not adventure. It's just work. They're tricking kids into building their own playground."

Adventure playgrounds do have downsides.

They're pretty ugly; they require a lot of space, and they need resources to staff and maintain.

And as with any playground, there is an opportunity for injury.

But the underlying philosophy of risky play can help kids live better lives.

For one thing, riskier playgrounds encourage more activity.

A study comparing playgrounds in London, where risky play spaces are popular, to those in San Francisco, Los Angeles, and New York, found that children using London's playgrounds were up to 18% more physically active.

The London playgrounds were cheaper and boasted fewer injuries, too.

And multiple studies have shown that children who engage in risky play have better risk detection, creativity, and self esteem.

The playground is one of the only kinds of architecture designed specifically for children.

And if the standard model we've decided on is seen as boring by its users, that's a problem.

Better design can fix that, even if it's a little risky.

I had to look through so many pictures of playgrounds for this story that I decided to use Wix to create a website collecting all of the ugliest and saddest pictures of playgrounds that I could find.

And now I have a perfectly curated arrangement of pictures of playgrounds next to graveyards and slides leading into dumpsters and whatever these kid-friendly statues are.

If you're looking for a simple way to share your passion about broken infrastructure or whatever it is that you're into these days, you should absolutely head to Wix.

To create your own website just like this, click the link below.

Wix does not directly impact our editorial, but their support makes videos like this possible.

So check them out.