Kristallsaal is a walk-through jewellery hall that runs entirely in the browser: six vitrines of cut-crystal pieces under museum lighting, a mirror-polished floor, and light that actually splits into colour inside the stones. There is no engine download and no build pipeline — one HTML file, one JavaScript module and Three.js, served as static files. It exists to answer a client question with a demo instead of a slide: what does "3D product presentation on the web" feel like at the high end?