Caverns contain occasional Underground Cabins where valuables can be found, as well as Glowing Mushroom biomes, mini-biomes like the Spider Nest, and occasional traps. In the lower areas of the Cavern layer, pools of lava can be found.

The Cavern layer is the largest layer. Its backdrop is the same as that of the Underground, except the dirt is of a darker hue, resembling stone. It contains the Ice biome, Underground Jungle, and Underground Desert biomes, which are each located beneath their surface versions, as well as Underground Glowing Mushroom biomes.