The Cave biomes have different types. Caves can be found all the other biomes even in the Toxic Zones. The difference between the caves will be regarding in its biome (mountain, marine, river, …). Here some examples:
SEA CAVES & SUBMARINE CAVES
The Sea Cave biome has zones full covered with water, others that will be flooded with the tides and others that are without water, but that will be still wet, so it will have drops falling from the ceiling. The walls are covered with barnacles and seaweed. There are some zones of the ground are covered also with seaweed that is slippery and can make the players fall if they are running.
The Submarine Caves have the most part of their zones underwater, but some have some parts without water, even with corridors and labyrinths. These caves are dangerous with aggressive fauna like Sharks or Giant Squids.
The River Cave biome is wet biomes. Some are abandoned water mines, salt mines or coalmines, flooded in some zones and full of bioluminescent mushrooms. In these caves the players can found Foxes, Bats or Wolfdogs.
The Mountain Caves have intricate labyrinths that go up and down. Some of these caves are also abandoned mines or abandoned Rites’ Villages. These biomes are the ones with some of the High Difficulty Areas with high-level enemies and fauna. The caves have lots of flora and fauna, creating in inside the mountains mini-ecosystems.
BUNKER & THE ABANDONED SUBWAY
The Bunker biome are places where the Radicals and the Contrabandists keep their goods. These are small places hidden inside of caves, farms or forests.
The Abandoned Subway is in its most part sunken, however, there is a small fraction that is still on the surface, under the Anarchy 01 in Sagrado. This is a dark place that has the rests of the Underground City, Pinky Pony (:D).