Caves (synonyms: caverns, holes, pits; fictionalized examples: The Cave of Seven Wonders, The Serpent’s Throat, Mugmire Caverns) are subterranean spaces either dug out by an animal or created naturally by some geological process. Caves may be cenotes. They may contain underground chambers, chasms, underground rivers, underground lakes, and crystal formations. Often in fictional worlds caves will lead into abandoned mines, underground ruins, old smuggler’s tunnels, or subterranean cities. Caves may collapse in narrative worlds and in game-oriented worlds they are often dungeons. They may be home to beasts, monsters, spelunkers, and trolls.

When designing caves for a fictional world, consider how the cave is laid out in three dimensions. Caverns will often drastically change elevation and abrupt vertical drops may exist. If you are designing a cave that will be explored, consider what sources of light may exist. Fictional caves will often include glowing rocks, crystals, creatures or fungi.