Below the surface is a maze of large structures. One of them being a cavern. Caverns are caves and tunnels that are automatically generated under the ground in various places. Caverns are composed mainly of stone, and contain large amounts of ores. In caverns underneath deserts or beaches you can see sandstone plotted around.

As well as caverns, you will also find ravines. Ravines are tall, long cracks of air, usually measuring around 30 to 50 blocks in height, making them quite dangerous if you fall down them. However, they are narrow and are usually no more than 5 blocks wide. Ravines can have small ledges along the top, which can be handy when making your way across lava or large amounts of water. Ravines can be found at any level and also sometimes appear on the world surface. Also known as canyons, these revines can be a serious hazard when wandering around the countryside, as they may not be obvious until one is right at the edge... or over it. Canyons do, from time to time, appear underwater where safe entry is possible. They can go very deep underground, sometimes spawning slimes or exposing diamond ore. If they reach deep enough, they may also be floored by the lava lakes at level 11. In the Amplified world type, ravines can reach from surface level to bedrock. Ravines can connect to caves, dungeons, abandoned mines, and any other generated structures. Due to the large surface area of their walls, ravines often have water and/or lava flowing down them (from springs in the walls, underground lakes, or even openings to the sea). For a safe desent down these revines you can add your own waterfall(s) from the edge but be aware of potential threats such as lava flow and hostile mobs.

The next generated structure that can be found underground is the Abandoned Mineshaft. Abandoned Mine Shafts are structures generated underground which consist of branching mining tunnels with wooden supports and broken rails passing through it. This is also the only place in Minecraft where venomous Cave Spiders can be found. It is easy to get lost in these labyrinths if torches or other reminder blocks are not placed. Open areas generate with bridges instead of leaving floating platforms. They contain minecarts with chests that may have rare items such as diamonds and horse armour. They may also contain iron ingots, coal, pickaxes, and other useful items. They are likely to expose veins of coal, iron, lapis lazuli, gold ore, and rarely, emerald and diamond ore.

As well as the above, you will also find dungeons underground. Dungeons are small, one-room spaces bordered by mossy cobblestone and cobblestone and typically contain chests with rare items with a hostile Monster Spawner in the center which guards the chests. The monster spawner can spawn either zombies, skeletons, or spiders. Occasionally, you may find that the mob spawner is covered with gravel and will be harder to reach and yet the mobs can still spawn with the gravel around it. Usually, placing a torch on the spawner will prevent mobs from spawning. The chests may contain rare valuables such as music discs, enchanted books, saddles, horse armor, and golden apples. Rarely, there may be two dungeons generated right next to each other. This can make two dungeons in only about one space. There is a small chance of not getting a chest.

The final structure is known as a Stronghold. Strongholds are structures that contain multiple rooms, doors and other aspects (some of these rooms include libraries, fountain rooms, dungeon-like rooms, etc.). They are made out of stone brick, mossy stone brick, cracked stone brick, doors, iron bars, Monster Eggs and stone slabs. They also contain silverfish which you should be careful of when digging around in strongholds. Portals to The End are found in specific rooms in strongholds. Chests may be found containing loot. 3 Strongholds spawn per world, which makes them rare to find. Strongholds can be found by right clicking an Eye of Ender, which will be thrown into the air and point the direction where the End Portal is, showing the way to the Stronghold.