In the 1930s, Danish landscape architect Carl Theodor Sørensen noticed that his neighborhood's children loved playing in old building sites. Watching kids swing from exposed beams, scavenge for scrap materials, and hammer together bridges inspired him to transform an abandoned housing estate into a dedicated junk playground. Sørensen's site became a huge success, and soon countries throughout Europe were making playgrounds out of derelict building yards and even former World War I bomb sites.

These environments might look dangerous, especially to 21st century parents who tend to be far more anxious about their childrens' safety than previous generations. But research has found these seemingly scary setups teach kids important lessons that standard playgrounds don't. Play is profoundly important for childhood development. Creating games and following rules helps teach problem solving. Moving our bodies through varied terrain helps hone our motor control. And playing with others lets us practice language and refine our social skills.

Since play comes naturally to all of us, children are likely to develop these skills in most environments. But researchers have identified a few factors that can maximize these benefits. Chief among them is freedom. Play is all about experimentation, and kids need the agency to explore and shape their surroundings without adults getting in the way. The next factor is novelty- kids are always hungry for new and unpredictable play elements. Finally, they need time to see their plans through. While we could all use more time to play, the best play environments offer freedom and novelty

that kids can explore as much or as little as they like. But traditional playgrounds don't offer much flexibility here. Swings, slides, and climbing frames are hardly novel structures. They also have relatively low affordance- a term used by play researchers to indicate how open-ended an object's design is. Items with high affordance, like a sandbox, can be interacted with in many ways. Meanwhile, objects with low affordance, like a slide, were designed with a single use in mind.

Even when kids are creative enough to find new uses for low affordance objects, they're still more limited playthings. To address these problems, some designers are looking back at Europe's junk playgrounds to create modern adventure playgrounds- big, open spaces full of high affordance structures and free play possibilities. Berlin's Kolle 37 features scrap and building tools for kids to manipulate. In Tokyo's muddy Harapa Park, children shape water slides, sink holes, and splash pools out of the natural landscape. And in London's Glamis Adventure Playground kids burn things in fire pits, with the help of play worker employees. While some parents worry these unpredictable spaces are too dangerous, play researchers like Ellen Sandseter

would say this so-called risky play is essential. Giving kids the space to experiment with fast speeds, high heights and getting lost helps them develop better judgment and confidence. In fact, risky play is how kids learn to manage risk and keep themselves safe. One study even found that kids were more likely to get seriously injured in traditional playgrounds- perhaps because adventure playgrounds encourage them to be more aware of their surroundings. Risky play also helps develop skills for managing mental health. Experimenting with small doses of uncertainty gets kids used to life being unpredictable, helping them better manage anxiety for years to come.

Adventure playgrounds aren't the only places for risky play. Nature playgrounds encouraging kids to explore creeks, caves, and tree climbing combine the perks of risk-taking with the health benefits of connecting with nature. Meanwhile, other designers are working to bring more freedom and novelty to traditional designs. This Philadelphia park features a 30-person mega-swing, and Nebraska's Omaha Riverfront Playground uses a ribbon of multi-layered decking as a play spine, warping up and down to reveal secret tunnels and rope forests. So the real key is to design a variety of playgrounds, supporting a wide range of activities that promote fun, agency, and a dash of uncertainty- inviting kids to fill in the possibilities.