This looks like a $20 indie game. It's a single HTML file.
No game engine. No libraries. Not even three.js. Claude Opus 5.5 wrote its own 3D renderer from scratch, then used it to build a fishing harbour floating in the sky.

Details it added:
- boats that rock on real waves (they read the water height under the hull)
- a lighthouse that sweeps the bay at night
- people who open umbrellas when it rains
- a waterfall pouring off the edge of the island

Click the water and the ripples bounce off the quay. I can't stop doing it