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, time in the world above continues to pass and vice versa. 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 the batilisks can move to the surface):
 * Cave Spider
 * Spitter
 * Batilisk
 * Bunnyman
 * Slurtle
 * Snurtle
 * Rock Lobster
 * Beardlord
 * Splumonkey
 * Tentapillar

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, the Cave Banana Tree, Fern, the Mushtree and its Red and Green counterparts.

Stalagmites are a common sight in any cave, and can be mined for Rocks, Gold, and Flint. 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.

Like on the surface, Set Pieces appear in caves too; often with a skeleton, and even with advanced buildings (like refrigerators, science machines, chests).

Death in Caves
Dying in a cave will cause the player to respawn at the Sinkhole they entered the cave through. Their items will remain in the cave. As of the "It's Not a Rock" update, dying in a cave will also result in the player's health, hunger and sanity being reduced to 50.

As well as this, any perishable items the player was 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. However a Lantern will be reduced to 0%.

Cave Regen
When the player clicks on a Sinkhole, and has already been down there before, the option appears for the cave to be regenerated. This means that the whole cave will be newly generated upon entry. This is very useful due to the fact that some players may have already explored the whole cave, and also this will allow new features from updates to spawn. In addition, this means that many essential resources are now renewable, whereas previously they weren't. For example, berry bushes are found in caves - the player could dig as many as they wanted with a shovel, and then regenerate the cave, so there would be more brand new ones.

Trivia

 * Caves were added in the May 21st Underground update.
 * Caves are expected to be a massive project and will be expanded throughout several updates.
 * Chester has a separate inventory in caves. It is unknown if this is a bug or not.
 * The Miners Hat is extremely useful in the Caves as it provides a constant light source.
 * Pigs cannot be taken into the caves. However a Pig House can be built underground and will spawn pigs as usual, although they will stay in their houses acting like its night, or constantly sleep when the house is destroyed.
 * There are also Cavewalls outside of the map.

Bugs

 * When an earthquake occurs, some items will fall in the walls, making them unreachable and causing Slurtles to be unable to reach them.
 * After sleeping in a cave, the morning tune and evening tune play at the same time.
 * Dying in a cave will result in the player waking up outside on the surface the morning of the next day, making it possible to make the days progress quickly in order to gain XP for characters with little trouble at all.
 * You can sleep in a tent repeatedly to cheat to higher day counts.
 * Spending enough time in caves can sometimes allow all grass/berry bushes to respawn their items making farming grass and berries very successful.