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 above) 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, Batilisks (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 Charlie. Some natural light does leak in from the surface at places, however, and there are other light sources as well. When the map is opened, players will see a new set of icons and terrain specific to the underground (pictured at right).

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 Red, Blue, Orange, and Yellow 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 and Snurtles leave their homes and roam the Cave in search of rocks to eat.

Creatures
In addition to normal Spiders, Fireflies, and Tentacles, the following creatures reside only in Caves (although the Batilisks can move to the surface at dusk):
 * Cave Spider
 * Spitter
 * Batilisk
 * Bunnyman/Beardlord
 * Bunnymen can be found above the ground only if the player builds Rabbit Hutches, which will spawn one Bunnyman per Rabbit Hutch.
 * Slurtle
 * Snurtle
 * Rock Lobster
 * Splumonkey
 * Big Tentacle
 * Slurper

Features
Some surface plants are also found in caves, such as Saplings, Evergreens, Berry Bushes, Grass, and Mushrooms. Additionally, several plants only grow underground: Light Flower, Cave Banana Tree, Fern, and Mushtree and its Red and Green counterparts. Like the aboveground versions, Berry Bushes and Grass will regenerate after a few days.

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, which can only be destroyed with a Pickaxe. Less common are the Slurtle Mounds, which spawn slow-moving Slurtles and rarely, Snurtles. Another feature is a Lava Pit, which is a renewable light source.

Like on the surface, Set Pieces appear in caves too, often with a skeleton, and even with advanced buildings such as Ice Boxes, Science Machines, and Chests.

Death in Caves
Dying in a cave will cause the player to respawn at the Sinkhole they entered the cave through the morning after the player's death. Items will remain in the cave, in the spot the player died. 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, as well as any clothing repairable with the Sewing Kit, impossible. Any Lanterns left will also be reduced to 0%.

Cave Regen
When the player clicks on a Sinkhole they have already entered, 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 it will allow new features from updates to spawn. In addition, this means that many more resources are now renewable, whereas previously they weren't. For example, Mandrakes are found in caves - the player can pick all of them and then regenerate the cave, and there will be more in a whole new map. However, cave regen may be removed, because it was originally meant for the early alpha caves to be able to have new features, and so when the caves are finished, there will be no point in new generation.

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.
 * Pigs cannot be taken into the caves. However, a Pig House can be built underground and will spawn a Pig as usual, although it will stay in its house or constantly sleep when the house is destroyed.

Bugs

 * After sleeping in a cave, the morning tune and evening tune play at the same time.
 * If the player starts a fire above the ground and then goes underground, no matter how much time is spent in the cave, the same fire will still be burning upon the player's return.