Wow. Messenger is beautiful!

Honestly I wouldn’t call that a website. It’s a 3D game that runs on the web.

If you count game demos on the web, then Epic Citadel, based on the port of Unreal Engine to various mobile and web platforms including HTML5/WebGL/asm.js, had a much detailed and more 3D world - it used all 3 dimensions fully, unlike OP which appears to be a flat world that’s quite restricted vertically. That demo first came out about 15 years ago, with the HTML5 version coming out a few years later.

Since then I’ve seen several other sites along similar lines, since Unity released a similar capability, but I haven’t kept track of them. The problem is they’re all essentially games that are more impressive for their look than their functionality, so they tend to have a spike of interest when people first see them and then you never hear of them again. And typically, the tech bitrots and the sites stop working after a while.