How do I create a 3D game for an outdated web browser?

Don’t forget to test primarily on IE6! That browser was notorious for handling things differently back then, so it's crucial to make sure your game runs properly on it.

Java applets were a common way to tackle 3D game development in that era. Using LWJGL could also be a solid option if you're comfortable with Java programming!

Using Flash or Java applets might be another path to explore if you're considering 3D since they were popular at that time, but keep in mind integration and support issues!

Raycasting could be a fun route! I created a basic raycasting game in JavaScript back in the early 2000s, and it can be quite straightforward. You could use vertical strips to represent the game world. You’d need various layers for different wall heights, but it’s doable and should work well even on older systems!

For a more serious approach, check out Macromedia Director. Though it's outdated now, it had decent 3D support back in the day. Just remember, back then web browsers were all over the place—what worked in one might not work in another! You could potentially fake 3D with pre-rendered sprites or SVGs since true 3D was pretty limited back then.

If you're aiming for a retro look, consider using VRML for your 3D visuals. It might not be the most advanced, but it fits that aesthetic perfectly!