images above showing how you create the cave.

where you put the invisible light by buhudaim, makes all the difference
Meshes converted and edited by me, from just-jasper

Roof 2 pieces, walls 2 pieces (curved and flat)
1 side only, to not make your game slow as hell

I was not satisfyied with the other cave that i did, sims couldn't enter and walk inside of it, so i did this one. Now your sims can live inside of it \o/

You find them in: rocks on build mode