In Seoul, a metropolis with a population density twice that of New York City, recreational spaces are at a premium. High demand for tennis and basketball courts can result in two-month wait times, says local architect Ji Hyun Park. Not content to wait around, Park and his firm, B.U.S. Architecture, designed "Undefined Playground," a fold-out, pop-up sports facility that Park says you can install anywhere.

Undefined Playground's utility is remarkable. In its folded configuration, Undefined the five-sided, wood-paneled steel frame covers 158 square feet and stands almost 12 feet tall. It looks a little like the free-throw booth at a carnival—only instead of one hoop, Undefined Playground features three. There's also a small soccer goal and a wall full of discus targets. The inside can serve as a storage space or, during ticketed events, a sales booth. Unfold it, and the number of soccer goals doubles. It can also, oddly enough, become a hammock, thanks to the nets that come with the structure.

B.U.S. Architecture

The project was born from a personal need (“We love sports,” Park says), but it has potential for cramped city dwellers everywhere. “Many cities, including Seoul, are suffering similar problems like lack of space, high density...competition to occupy space from retail, offices, and [residential buildings.]” As developers strive to build as many condos as possible, there will inevitably be fewer public-provided places for play, and it’s not like high-rise apartments come with basketball hoops out back.

B.U.S.’s solution for this problem comes with a charming side effect: by letting its users play a bit spontaneously, almost anywhere, Undefined Playground mimics the way kids will turn the built environment—an empty alley, the side of an apartment building—into a court of their own. “As I recall, when I was young, anywhere in the neighborhood would become our playground, as long as we had a ball,” Park says. And when you’re done and worn out, there’s always that hammock feature.