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.

Undefined Playground s utility is remarkable.

It looks a little like the free-throw booth at a carnival—only instead of one hoop, Undefined Playground features three.

It can also, oddly enough, become a hammock, thanks to the nets that come with the structure.

Many cities, including Seoul, are suffering similar problems like lack of space, high density…competition to occupy space from retail, offices, and residential buildings.

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