Jantar Mantar is a playground of epic proportions: 19 enigmatic structures made of yellow stone and marble are scattered across 4½ acres in the central Indian city of Jaipur. They are perfectly proportioned for youthful exploits. Visiting as children on a school trip, my friends and I clambered up and down the enormous staircases, darting from edifice to edifice and chasing each other between patches of grass under the open skies and baking heat of Rajasthan. The site’s historical, scientific, mathematical and architectural significance was somewhat lost on us.

In the modern era, Jantar Mantar—roughly translated as “calculation instrument”—has become a tourist attraction and a UNESCO World Heritage Site, restored several times over the past 300 years. It was originally built ...