You can find a large number of Caves all over every Creativerse-world. They seem to be more or less random to simulate "natural" shapes. They are not specifically designed to help you find Nodes of Ores easily nor are they "dungeons" with special findings at their ends or so.
Most Caves have small entries and are rather tunnels at first that won't lead far, not deeper than into the Fossil layer with Coal Nodes and/or Obsidian Nodes to be seen - these caves might often just barely touch the upper parts of the Stalactite layer. Only few longwinded caves lead from the surface to the Lava layer, and extremely rarely even into the Corruption layer, which is currently the deepest underground layer.
In the darkness of caves Night Pigsies and/or Night Rocksters might spawn on Limestone, Bedrock or on Ore Nodes - even during the day, despite their names (night creatures), as long as their spawning-spots are dark enough. They are also able to come out from these caves during the day if they can sense/see a player character nearby.
You can sometimes find Stone Treasure Chests randomly spawning in the darkness there too.
On little bits of Siltstone and/or Stalactite also ordinary green Mirus might appear and then ascend into upper parts of the caves or might even exit the caves onto the surface.
All of these creatures - Night Pigsies, Night Rocksters and Mirus - cannot stand the sun. They will all burst into blue flames when hit by sunlight and perish after a few seconds without leaving anything behind.
Fewer caves will lead further down into the Stalactite layer with lakes of Mineral Water and/or Iron Nodes and rarely also Diamond Nodes to be found. There you might able to find a number of larger caves in the shape of big underground-holes connected to each other. Some of these are not connected to the surface, but you might find them when digging your way.
There, on Siltstone, Stalactite, Tourmaline and/or several Nodes, Mirus and/or even Warmworms can spawn in darkness. Warmworms are resistant to sunlight, but will not spawn in caves lit by artificial lighting.
On the Stalactite layer, Obsidian Treasure Chests are randomly able to spawn in the dark.
Only very few cave-tunnels that lead downwards from the surface might even have chasms that can make player-characters fall down into the dangerous Lava layer with it's lakes made of liquid Lava and a rising heat-scale that will culminate in fire-damage when it has filled with red color.
On this fiery layer, Warmworms and also Hot Feet can spawn on Igneous Rocks, Hardened Lava, Sulfur, Nodes and/or other types of rocks. Hot Feet are dangerous enemies, but will burn away in sunlight if they ever reach the surface. In the Lava layer a number of large hole-like caves can be found, more rarely connected to each other than the caves on the Stalactite layer with not so many tunnels as it seems.
Iron Treasure Chests can rarely be found on the Lava layer, randomly spawning in this relative darkness. Artificial lighting will prevent these chests and all creatures from spawning, but neither the glow of hardened lava nor that of liquid lava can prevent any spawns.
Nearly no caves are known to lead from the surface to the (current) deepest parts of the Creativerse-gameworlds, the Corruption layer. The Corruption layer is in principle one giant cave spanning all over the world underground.
Still sometimes you can find larger bodies of corrupted rocks connecting the ground and ceiling of the Corruption layer, additional to occasional rocky pillars, stalactites, stalagmites and the net of wooden roots and/or brances that grows on the inside of this giant cave-layer.
Some caves can be dangerously deep chasms, a few will have them near the entrance or might lead downwards horizontally from the very beginning; which occurs mainly in the Mountains or also in Canyons where cave-entries can sometimes also be a lot larger than usual. Caution is to be exercised. Flares might come in handy.
Some seemingly giant caves might turn out to be mere recesses into hills or mountain-sides (often with rivers on their base) at closer inspection, however other recesses might lead to the entrances of actual caves of smaller size.
Still even in mere recesses night creatures and also treasure chests are able to spawn on the same types of blocks as in "normal" caves, just as long as it's dark enough.
Caves in snowy parts of the world, like on Mountains, snow-covered Canyons, Taigas or Frozen Deserts can be a good place to warm up if the coldness-scale has been dangerously filled with white already.
Some caves may feature Stalactites growing from their ceilings even in upper parts, mainly caves that lead downwards from sandy Shores or Canyons.
Quite often cave-entrances can be half-hidden by trees. It's not uncommon for Red Mushrooms, Tundra Flowers, Cacti or other plants to grow at cave-entries a few "steps" further down than the surface.
If caves are close to bodies of Water from Oceans or Bog Water from Swamplands, these liquids might run down partways into the caves; usually not very far though.