From Tom Scott.
Well before the first climbing frame was patented as "jungle gym", mathematician Charles Hinton thought they might be able to teach kids four-dimensional thinking. ■ Thanks to the Winnetka Historical Society! More from them: https://www.winnetkahistory.org/gazette/j-is-for-jungle-gym/
Original patents referenced:
Also referenced is "Winnetka: The history and significance of an educational experiment", by Washburne and Marland.