When my kids were younger we used to go to nature classes at a park about a half hour away. When the weather was nice, the homeschooling families would stay after, and our children would play under the trees and brambles surrounding the nature center. There was an old playground at the other end of the park, about a ten to fifteen minute walk, but it never seemed necessary to trek over there. The children had plenty to play with. Our side of the park had a copse of tall pines that made the best hangout. Some of the kids had actually climbed fifteen feet up in those pines. The ladder-like branches made it easy for them. Sometimes they found owl pellets among the bed of pine needles at the base of the trees. They carried home pine cones in their pockets and pine tar on their pants. A hill beside the trees made the perfect sledding hill in winter, and if that didn't hold your interest you could walk over to the river and see what treasure high tide left upon the shore.
At some point, the county decided to add a playground to our side of the park. It was newer and shinier than the other playground, with lots of climbing apparatus, slides, and a plastic wall with pretend fossils hidden underneath. The county planted native trees and shrubs around it to help it blend in. The first thing our children noticed was that the playground was right at the bottom of the sledding hill. Luckily, it was spring, so they recovered pretty quickly from that disappointment. It was shiny and new, after all. Eventually, however, all but the littlest of our group were back in the trees. That would always be where they played the most.
Playgrounds are fine for a short time, but they are limited in how children can use them, just like any themed or educational toy. The natural world offers much greater opportunities for exploration and adventure.