Caves

Caves are large underground sections of the world filled with unique features. They are so large that they are generated as whole new maps upon entering. Caves have their own artwork, terrain, and maps. Various creatures, plants, and other objects reside within.

Spelunking
A Cave can be found underneath a Plugged Sinkhole. Upon mining the plug, an open Sinkhole appears with a rope leading down into a new Cave. Each Cave is generated just like a new world. A different loading screen (pictured) will play while it is created. While within a Cave, the world above freezes in place but will resume when the character returns. Once a Sinkhole is unplugged, Cave-specific creatures (see below) can emerge at Dusk and roam the surface world.

Each Cave begins in a small circle of light with a rope hanging down and a skeleton at the bottom. The world within a Cave is always considered to be Night. This means that Sanity slowly reduces and in areas of complete darkness characters are vulnerable to the Grue. Some natural light does leak in from the surface however, and there are other light sources as well. Camera control is necessary because of the Cave walls. When the map is opened, players will see a new set of icons and terrain specific to the underground (pictured).

Earthquakes
While underground, the player may experience Earthquakes. When this happens, the screen shakes and a rumbling sound plays. Rocks, Flint, Nitre, Marble, Gold Nuggets, and sometimes even Red and Blue Gems, will fall from the Cave ceiling. Each of these is preceded by a small shadow and causes damage if it hits the character. Once the earthquake ends, Slurtles, Snurtles, and Spiders leave their homes and roam the Cave in search of food.

Creatures
In addition to normal Spiders and Tentacles, the following creatures reside only in Caves (although some can later move to the surface):
 * Cave Spider
 * Spitter
 * Batilisk
 * Bunnyman
 * Slurtle
 * Snurtle

Features
Some surface plants are also found in Caves, such as Saplings (common), Evergreens, Berry Bushes, Grass, and Mushrooms. Additionally several plants only grow underground: the Light Flower, and the Mushtree.

Stalagmites are a common sight in any cave, and can be mined for Rocks and other items. Similar looking Spilagmites are home to Cave Spiders and Spitters, and can only be destroyed with a Pickaxe. Less common are the Slurtle Mounds, which spawn slow-moving Slurtles and Snurtles.

Trivia

 * Caves were added in the May 21st Underground update, but are still in Alpha.
 * Caves are expected to be a massive project and will be expanded throughout several updates.
 * When you die in a cave, you respawn on the surface just outside the Sinkhole. Your items are still in the cave.
 * When you die in a cave, any light source you have will have despawned.
 * When you die in a cave and return to the surface, any perishable items you may have been carrying instantly turn into rot, making the recovery of gathered light bulbs or food you may have brought with you impossible. This includes any clothing that is repairable with the Sewing Kit.
 * Chester has a separate inventory in caves. It is unknown if this is a bug or not.
 * When you sleep in a cave, you will hear the tune of the morning, and the tune of the evening at the same time (Bug?)