“What Are Adventure Playgrounds? In short, adventure playgrounds are places where children can create and modify their own environments, rather than relying on rigid equipment that only serves a limit set of programmed purposes: “In a sense, you and I have always played in ‘adventure playgrounds.’ We created a fort in the kitchen cabinets, jumped from couch to couch across oceans; we snuck out through a hole in the fence to a new world. We climbed trees and hid in bushes. We played in the mud and the rain. We chased each other, made secret worlds …” (via WebUrbanist » Urban Adventure Playgrounds: The Coolest Places You Probably Never Played as a Kid)
When I first saw these I thought, “Man, if I were 10, I would have killed for a playground like that.”