Build an interactive 3D Stonehenge scene in the browser from one prompt

A Redditor gave Claude Fable 5.2, on high effort, one prompt asking for an interactive Stonehenge scene. The result is a single HTML file using three.js that runs in the browser. It includes the sarsen stones and trilithons with lichen, the bluestones and the Heel Stone, a chalk field with instanced grass that sways in the wind, real-time shadows, a sun that follows the summer solstice path, 144 low-poly visitors and an "as built" view of the complete monument. The poster published it as a live page on GitHub Pages.

The scene works and is online to try. The poster gave a full cost breakdown: $21 in total across 20.3M tokens, most of it cache reads (19.4M tokens, about $4), cache writes (564K tokens, about $6) and output (286K tokens, about $11). The post gives no account of bugs or how many rounds of fixing happened inside the run.

The token count shows a long agentic run, not a single reply, but the poster did not say which harness drove it; only the model is named. A one-prompt build at this size cost about $21, mostly output and cache writes, so budget for that before trying a similar scene.