It's all shaders! That's why they take up so little memory space. Here's a video where IQ explains how to "model" a greek temple using this technique: https://youtu.be/-pdSjBPH3zM?t=303

And here's a very high-level video about wondermoss in particular (archive.org link since the original appears to have been removed): https://web.archive.org/web/20140718035429/https://www.youtu...