Caves can be found naturally in any Biome. Caves can contain Feral Zombies, Mushrooms, exposed Ore, Stalactites, and Stalagmites. Every cave contains an Apache Artifact Chest, and may also contain a Gun Safe or a Munitions Box.
Cave layouts are not randomly generated there are just four different cave prefabs that can spawn.
With the introduction of caves, cave exploration (Spelunking) and mining have becomes the most efficient means of obtaining mineable resources. Large veins of Ore are commonly exposed in cave walls, making their harvesting quite easy once found. The trade-off is that caves are widely spaced apart in the world, and usually in the middle of nowhere, requiring the player to travel from their established base to mine
Exploring a cave system can be treacherous so be prepared with sufficient resources and lighting. While most cave entrances are safe enough to descend, they make have steep enough slopes to cause the player to slip and fall. Larger caverns can have vertical drops, depending on where the tunnels intersect, so ladders or other climbing equipment is essential. Caves and tunnels often connect into massive tunnel systems as well, and can quickly become maze-like, so marking your trail is always a good idea.
Exposed mineral ores are common, but highly random, and do not seem to spawn in as frequently as before, nor are they always surrounded by a tell-tale coating of gravel. It may take a bit of exploring to find a specific ore, but there are usually large veins, even of Coal Ore and Potassium Nitrate, making the hunt well worth it. Another good practice is to always look up, because ore veins are as often as not on the ceiling especially in larger spaces. Stalactites and stalagmites also drop Nitrate Powder when mined.
Zombies will spawn in caves, and are home of the fearsome Feral Zombie, so keep your weapons on you. Hordes do not appear to spawn inside caves as of yet though, so Players can go sufficiently deep to throw off zombie AI, and need not fear a flood of zombies (note, this has not been tested on 'feral' 7th nights. Which make all players hunted no matter where they are located in the world).