However, since the large majority of areas in Caves are completely dark, players will need to bring their own sources of light to be able to effectively explore. Permanent or semi-permanent light sources can be found from certain objects that naturally occur in Caves, such as Light Flowers, Mushtrees, or Nightmare Fissures.

Some natural light may leak in from the surface in certain places, but these sources of light will only appear while it is daytime in the world above. This means that Sanity slowly drains while in Caves and, in areas of complete darkness, characters are vulnerable to Charlie. However, Caves are perpetually in darkness.

The worlds within a Cave are affected by the Day-Night Cycle, Cycle of the Moon, and the four Seasons. Interacting with the rope will return the player to the surface world. When a Sinkhole is entered (or 'spelunked'), the player will be dropped into a small circle of light within the Cave, with a rope hanging from above and a skeleton nearby. Once a Sinkhole is unplugged, Batilisks can emerge at Dusk and roam the surface world, but will not travel far from the Sinkhole from which they emerged. The Clock, however, is removed from the game's HUD while the player is inside a Cave, making it difficult to keep track of the current Day-Night Cycle. While within a Cave, time in the world above continues to pass and vice versa. A different loading screen (pictured above) will play while it is created. Each Cave is generated just like a new world. Each Sinkhole connects to a different Cave. Upon mining the plug with a Pickaxe, an open Sinkhole appears with a rope leading down into a new Cave. A Cave can be found underneath a Plugged Sinkhole.

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