Just drop 'em right into your Overgrowth folder. Should work just fine.
I made these models as practice once I got the hang of exporting, importing, etc., getting everything set up. They're actually pretty high-quality models, and the textures are 1024x1024 (although I wanted them to be higher) for performance issues I suppose. Here's all the models in the pack.
There's one "Cave wall" model (behind all the other models, it's a front and back view), two "bridge" models, designed specifically for multiple uses, some stalagmite models, as well as a single stalagmite, a pillar, a cave rock with mold, (in the front, it's a top and bottom view), and 3 "Small tunnel" Segments. A straightaway, a decline, and a turn. You can make some awesome scenes with it. With just those models I was able to make this;
The models are of-course W.I.P and not finished, but i'd be open for criticism as well as suggestions. Feel free to use them to tinker with. If anyone uses them, i'm excited to see what you people come up with as well.
I plan on making more and more models for Overgrowth, simply because of how fun and satisfying the system is. My next personal project will be a reptilian species, so i'm probably gonna stick around.
Sorry if I messed up some sort of format or something. These are my first models, lol.