Cave



Caverns or caves are commonly-found cavities in the stone layer of a map. Many caverns have tunnels branching off (called catacombs) and winding in other directions, some of which connect to the surface of the map creating natural entries to the cavern. Caverns can be quite deep, extending from the surface all the way to the bedrock layer. These caverns are randomly generated so no two of them will look exactly alike, making guides hard to be formed. They can sometimes be attached to natural dungeons.

Caverns usually contain at least one type of exposed ore block. Hostile mobs often spawn in naturally occurring caverns so it is advisable to bring along a weapon if on any difficulty other than peaceful. Cave systems are most often found in mountain biomes.

Caverns can be useful as a starting point for creating player-made dungeons and other underground structures. Since natural caverns have areas of exposed rock, they can save quite a bit of time while searching for ore. However, caverns can be quite deep, like pits, so accidentally breaking into one from above could inflict a lot of fall damage. Players should be aware of the potential presence of lava as it is one of the main risk factors of exploring caverns, even on peaceful.

Pits
A pit is a hole in the ground that falls straight down. Pits are usually found in caverns or when mining down you may fall into one. Pits are a good way to go farther underground, but are dangerous because they can lead into lava, a dungeon, or the fall may kill the player. It is advised that the player should bring a bucket of water or ladders which can be used to create a water elevator or stairway before exploring a pit. If you fall in a pit of lava you will most likely die and any items in your inventory will be burned. However, lava pools are only common near bedrock.

Finding caverns
There are a number of ways to find caverns. Below is a table, designed to make cavern-hunting easier.

Navigating caverns
It is surprisingly easy to get lost in caverns. Below are a number of methods you can implement while exploring to prevent this.

Markers
There are a variety of markers you can leave behind to make trails.
 * Mushrooms:  Relatively easy to acquire if you're near a swamp biome, quick to harvest and will attach to nearly any block.  Space them close enough together so the last one is still visible behind you when you go to place the next.  With red and brown mushrooms, you can have two separate trails that are easy to retrace.  When you're done with them, you might try some mushroom stew.
 * Torches: You can place all your torches on the right side of the cave when you enter a new passage.  This allows you to find your way back to the entrance simply by keeping the torches on your left. When encountering multiple caverns, also known as a fork, put two torches at the exit to indicate the correct way to exit the cavern.   You can also place torches to point towards the exit.  Disadvantages:
 * If a cave loops back on itself at some point, there can be some confusion as to the shortest way out.
 * Also, it is unlikely that torches restricted to the right side will provide sufficient light to completely prevent mobs from spawning, so you will probably need to place additional torches on the cavern floor in caves and the wider passageways.
 * Signs at intersections, often with "ASCII arrows", such as --> or ^, to indicate the heading. Keep in mind that you will need to be able to see these signposts the most on your way back out of the cavern, so when placing them, it is important to position them where they will be easily visible from the other direction. Signs are reliable (lava notwithstanding) but not cheap (6 wooden planks and 1 stick per sign), nor do they stack, making it difficult to bring enough signs for anything larger than a medium-sized cavern system. You can however bring stacks of wood, and a crafting table to make signs from them. The table can be retrieved and taken with you after each use.  Normally you'll want to carry logs, but in abandoned mineshafts, planks are especially plentiful.
 * Cobblestone arrows at each intersection, pointing back towards the passage you just came from. A torch can be placed on the block at the tip of the arrow to ensure that the arrow is easy to spot. This method has the advantage of utilizing a resource (cobblestone) that is common in caverns and easily carried in bulk, making it suitable for aiding in the exploration of even the most massive caverns. These arrows can be placed on walls or embedded into the floor, and can point in any direction. Similarly to the signpost method, cobblestone arrows should be placed in locations that are easily visible on the way back out of the cavern.
 * Cobblestone can also be used for walls or barricades to block off dead-ends or previously explored cavern branches to find exits more quickly. This along with the "right-side" torch method work very well hand-in-hand and can guarantee a less confusing exit strategy for players in a hurry to end their cavern run.
 * In otherwise "cleaned-up" caverns or mineshafts, dead-ends that have already been "cleaned out" can be marked with a block of dirt.
 * Redstone: If you're not using it for other things, you can make simple "trails" from spare redstone dust.
 * You can also use redstone torches by placing them regularly within sight of each other, they are very easy to see and you can easily follow the torches back to where you first started placing them.  Note that redstone torches do not provide enough light to stop monster spawning.
 * Minecart tracks can also be used to mark trails. Of course, if you've laid down an actual track, it's easy to follow or ride that to either end.
 * Jack-o-lanterns can be placed at intersections with the face pointing towards the exit. This is useful as it acts both as a direction out, but also is its own source of light. Jack-o-lanterns are easy to acquire once you start a pumpkin farm, and give off more light than a torch. In cases where there is one path on top of the other one, place the jack-o-lantern higher (using piles of gravel or some other temporary block to place it on top of) to indicate the exit is the upper path. Make sure to place them at the middle of the intersecting paths, with the pumpkin easy to see from both directions.
 * If you've been to the Nether, netherrack is conspicuous. It is also very quick to mine, and not naturally occurring in the Overworld. When going back, you can set them alight, recovering torches and marking explored paths.
 * Wool is versatile and stackable, and comes in a variety of colors; find a sheep, fence it in, and paint it with your favorite color to get a supply of wool in that color. Use different colors for different symbols, e.g., "red" for "explored branch", or a combo of "white" and "yellow" to form an exit sign arrow. Beware that wool is flammable.

Other hints

 * While it will not help you in navigating the cave itself, it may be wise to bring a map with you into a large cave, should you get lost and need to dig your way out. Note that most caves occupy less area horizontally than they might seem, but interconnected caves and abandoned mineshafts can sprawl over huge distances.  You might well map some new surface as you explore underground, but the cave itself will not be mapped.
 * An important tip to remember in caves is to always look around, especially upwards. One of the most common sources of mobs within previously explored caves is unnoticed openings in the ceiling or walls. If you're in a ravine, watch out for monsters falling off of high ledges!
 * A good mining practice is to fully explore and light a cave system before beginning to mine out any resources. It is extremely dangerous to stop and mine in a dark cave system, and you can lose your loot if you are killed. Check for "broken bridges" such as gravel masses or 2-block drops.  If monsters can come out of them, you may want to change that; once verified safe, you can save the blocked-off areas for later.
 * As part of exploration, "clean up" the area, taking off leftover blocks, filling small pits, and generally smoothing things out. In abandoned mineshafts, clear out most of the fence-and-plank "supports" as you "claim" an area.  This will improve both visibility and mobility, cutting down on unpleasant surprises.
 * To reach ores or tunnels high on the ceiling, try pillar jumping to gain altitude. You can also build bridges across ravines and pits.
 * Water coming down from above is especially troublesome, as it can carry monsters down from a whole chain of darkened caverns.
 * It's a good idea to swim upwards and light the path of the flow.
 * Most water flows can be captured at the source with a bucket; if that doesn't work out, they can be contained with fences or blocks. Either way, be aware of areas where the water flow formerly blocked monsters!  Some flows may be useful to keep as water ladders.
 * Some water flows come from openings in the seafloor. With care (and perhaps a door or some ladders), you can swim up these and mark the entrance with a jack-o-lantern, which will generally be visible from the sea surface.  Such openings are also a quick way to get back to the surface if you've gotten lost.  With a bit more effort, you can seal the opening altogether, perhaps leaving a shaft with ladders for your own use.  (Remember that ladders and signs block water.)
 * When finished exploring a cave, you can make your own exit -- just dig upwards to the surface in a staircase fashion, watching for drips and being careful not to dig the block just above you.
 * When digging a staircase out of a cave, it can be useful to check your map to figure out where you will, or want to, emerge. Coming out into the seabed can be tricky, especially if your torches get washed away.

Classification of caverns
A cavern can be classified into the following kinds of cave systems.

Small cave (dud cave)


Small caves are primarily located close to sea level and are unlikely to be linked with other caverns. They frequently contain small deposits of basic ores such as coal and iron whilst seldom possessing rarer materials. Such caves may have multiple entrances which are naturally lit. This type of cave also commonly has a pool of water in it, likely caused by the generation of the water itself.

Medium cave (splatter cave)
Medium sized cave systems are commonly found within reach of other, often smaller, bountiful caverns which are accessible via mining. These caverns frequently contain large deposits of basic ores alongside small repositories of rarer materials - including Lapis Lazuli and Gold. Splatter caves also regularly contain, at the very least, minor water or lava flows as well as the presence of small dungeons.

Large cave


Large subterranean systems, found deep within the earth close to the bedrock, hold large deposits of essentially every known type of ore - with rarer materials, such as Diamond, being found, like everywhere else, in less frequent deposits than more common materials. Such systems contain a number of large lakes as well as the presence of major lava flows. Furthermore, exploring large caverns is often rather hard, due to the huge volume of naturally generated tunnels often part of epic caverns. It is common for dungeons to be found within these systems.

Circular rooms


During the terrain generation process large symmetrical and cylindrical chambers of various sizes can infrequently be created underground which often merge with other cave systems. Although not particularly of interest, from a mining perspective, they may appear unnatural and irregular in comparison to the surrounding terrain. Very rarely, a dungeon can be found in these rooms.

Ravine


Natural formations of stone and gravel that can cross a big part of an island. It's a bit deep, and sometimes can connect with any kind of cave, even with dungeons and sometimes abandoned mine shafts or, much rarer, strongholds. To ensure safety while proceeding downwards, use sand and gravel to drop down and create a basic elevator. You may also want to simply descend down a water fall. In the ravine, fair amounts of coal and iron ore can be found. Due to the fact the ravines are fairly deep drops, a good ten minutes may find a deposit of gold or rarely, diamond. Ravines were first introduced in the Beta 1.8 Adventure Update. It is very possible to die in ravines due to the large drops and connections to caves.

Deep cliff
A deep cavern sometimes goes down onto bedrock. This formation is not to be confused with a ravine, although they can be quite similar. These caverns are usually not linked to other caverns and don't have large amounts of minerals in them. Dungeons usually aren't linked to them because they are generated almost straight down and the bottom is often in full sunlight. This makes it hard for hostile mobs to spawn there. They are very useful for making traps or to lure mobs to fall to their deaths and safely collect their drops at the bottom.

Giant entrance


These caverns have a large hole for an entrance and then often spiral down, containing materials like coal and iron. These are not that rare and if you look hard enough, you can find one.

Lava lakes


Most often found in large caves far underground, lava lakes generally have the most rare minerals including lapis lazuli ore, gold ore, and redstone ore, sometimes even diamond ore. But lava lakes most often hold the common minerals such as iron ore and coal. If you have a bucket of water on hand, this can be a great way to obtain obsidian.

Bedrock level lava lakes tend to have deposits of diamond at their edges, so a good strategy is to douse the lake with water and dig around it.

Water lakes


Found in every part of the world at every level underground, water lakes are by far the most common lake. Water lakes occur on the surface, a mere 1-20 blocks below the surface, and from then on to bedrock.

History


Caverns are one of the oldest features in Minecraft and appeared in the 2nd Classic update, Pre 0.0.9a Cave game tech test when the game didn't even have a name.

In the Beta 1.8 Adventure Update, cave generation was changed, and caves were made much bigger and more common. Ravines, strongholds and mineshafts were also added in this update.

Caves and ravines did not generate in the Overworld in 12w07a and 12w07b, due to a bug.

Trivia

 * Sand and sandstone, as well as generated structures, can overwrite caves.
 * In jungle biomes, vines generate in caves near the surface.
 * Though ores are abundant in caverns and often require little digging to get to, ore veins visible in the walls of the cavern often contain little ore, as the cavern cut through them when it was generated.