Cave



Caverns, tunnels, or caves are commonly-found cavities in the stone layer of a map. Many caverns have tunnels branching off and winding in other directions, some of which connect to the surface of the map creating natural entrances to the cavern (and some of which lead to dead ends). Caverns can be quite deep, extending from the surface all the way to the bedrock layer. These caverns are randomly generated so two of them will almost never look exactly alike, making guides difficult to write. 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 because of its low light level, so it is advisable to bring along a weapon if on any difficulty other than Peaceful. Exposed 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, if not death to the player. 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 can be found if mining downward. 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 below Y-layer 13. Technically caves are simply pockets of air (ignoring fluids, lava lakes, and water lakes). This explains the "Dud" caves and caves that appear to "skim" the surface.

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

Navigating and surviving caverns

 * It is surprisingly easy to get lost in caverns. Below are a number of methods you can implement while exploring to prevent this, especially trail markers. The Navigation tutorial has much more information about markers and other navigation methods.  (Summary:  Torches, wool, signs, blocks and arrows made from them, and especially jack-o-lanterns.)
 * One fairly easy marker method is the "torch on the right" rule. While exploring a cave simply place torches on the right side of the wall as you go deeper in.  This way, no matter how complicated and even intertwined the caves get, you can always find your way back because if the torch is on the left of a cave wall, that means you're heading towards the exit. Conversely, if it's on the right, it means you're heading deeper in.
 * 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, wherer 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 safety is verified, 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, you can clear out most of the fence-and-plank "supports" as you "claim" an area.  This will use a lot of axes, but it will improve both visibility and mobility, cutting down on unpleasant surprises.  (Notably, those fences provide better cover for creepers than they do for you!)
 * 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 for travel—you can swim up or down waterfalls to traverse high cliffs.  With a little care, you can swim along the outside of the waterfall, which lets you keep breathing normally.
 * 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.)
 * In addition, one can create easy access from the cave to the ocean surface by making a pillar of sugar cane. This will provide a fast, breathable path in both directions.  This method can be used for both entering and exiting caves.
 * Lava flows and pools can also block your passage as well as the monsters'. Like water, lava flows can be bucketed if you can reach the source, or contained with blocks otherwise.  Lava pools can be flooded to convert them to obsidian.  Again, be aware of areas where monsters were blocked by the lava.  Also, remember to re-light the area after removing that brightly glowing lava.
 * When finished exploring a cave, you can make your own exit—just dig upwards to the surface in a staircase fashion, watching for drips. You can also dig directly upwards, however, be careful when doing so, as it can cause suffocation.
 * 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. Put your torches 3 blocks up instead of 2 or 1 to avoid "wash-outs" (specifically: high enough that the air 1 block above the next higher stair isn't beside the torch).

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

Trench
If a cavern generates high enough, it can remove some of the dirt and grass blocks while not being completely submerged, forming a "ditch" or "trench" type formation. A similar effect can be seen when a river biome generates above sea layer, leaving no water and a trench-erous trench.

Small cavern (Dud Cavern)


Small caverns 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 caverns 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 (Monster Nest)


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 sometimes thought that hostile mobs spawn more often here, but that is probably due to the fact that you can see farther in Large caves than in other types of caverns. It is common for dungeons to be found within these systems. Also large caves are very hard to explore due to medium and small caves spawning nearby. It is best to take extra precautions when exploring large caves, as they are often large and confusing.

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. These "rooms" vary from roughly 5 to 22 blocks in height, and from roughly 11 to over 30 blocks in width and/or length, though the latter is quite rare. Although not particularly of interest, from a mining perspective, they may appear unnatural and irregular in comparison to the surrounding terrain. While the smallest rarely contain many ores, the largest can be quite useful for mining as their sheer surface area rivals that of a medium-large ravine. Medium and large circular rooms may be used for growing Huge Mushrooms with little or no modification. Very rarely, a dungeon can be found in these rooms. Circular rooms can make good underground bases, just make sure you block off any other entrances and make sure that hostile mobs can't get in.

Ravine


These are natural formations of stone and gravel that can cross a big part of an island. It's rather 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 waterfall. 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 (Wormhole)


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. Rarely, these entrances can go nearly straight down, exposing rare minerals like gold and lapis lazuli.

Sea-access cave


These caves are often connected with the sea, and can be accessed from the sea. These were most common in Minecraft Classic. These act like a horizontal underwater giant entrance to a splatter cave that often contains lava, allowing them to be seen from the surface of the ocean. Back in Classic it was similar, however, rather than their entrance being at the bottom of the sea, their entrance would usually be a hole in the side of an ocean mountain, leading down to a cave pool.

Lava lakes


Most often found in large caves far underground, lava lakes are believed to have the most valuable materials near them; however, there is no proof that ores appear more around them. A lava lake can even cut through a vein of ore and reduce the amount of ore in the vein. However, if you have a bucket of water on hand, this can be a great way to obtain obsidian. Sometimes water can flow partway over them, producing a “conveyor belt to doom”: Not only can the water push you into the lava, but if you die in the water, your possessions will be washed into it as well.

Water lakes


Found in every part of the world, 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.

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.
 * Sand often will fall into caverns generated near the surface of a desert or beach and so craters in a desert will alert the player to caves below the surface.
 * On 'Get Satisfaction', "rainbow crystalline caves" were marked as a planned feature by Notch.
 * Rarely, near-surface caves can be generated with a grass (later turning to dirt with the darkness) floor. These are not real caves, but rather "closed-over overhangs", generated only in Extreme Hills. These are technically inverted floating islands.
 * Ambience noises can be caused by dark caves.
 * One of the earlier versions of the Xbox edition had "Magic Blue Caves". These were actually normal caves with an eerie blue light (moonlight), caused by a bug which allowed surface light to shine through the edge of the map (+ or -431). Without knowing about the bug most players could not work out why the cave they just discovered was bathed in blue light. With daybreak the sunlight on the walls combined with the presence of the worldwall made it much more obvious what was happening.