Minecraft/Structures

Dungeons
Dungeons in Minecraft (not to be confused with the separate game Minecraft Dungeons) are small enclosures made of cobblestone or mossy cobblestone that generate underground. They have a spawner that spawns either zombies, skeletons, or spiders and one or two chests containing rare items. The spawner can be disabled by surrounding it with several torches, broken for XP, or used to set up a mob farm.

Abandoned Mineshafts
A group of underground tunnels with cosmetic wooden supports, rails, minecarts with chests containing rare items, and cave spider spawner. The spawner can be disabled by surrounding it with several torches, broken for XP, or used to set up a mob farm. (However, a cave spider farm is incredibly difficult to contain.)

Desert Temples
An aboveground structure in deserts made of sandstone and terracotta. It consists of a pyramid and two pillars, all hollow. There is a 3x3 hole in the center of the pyramid, with a blue terracotta block covering the center. DO NOT BREAK IT. There is a pressure plate that activates 9 TNT in the center. Surrounding the pressure plate is 4 chests with rare loot, and the TNT can be taken as well.

Jungle Temples
A cobblestone structure in jungles with multiple floors, some chests, and traps. There is also a lever puzzle, but due to the nature of Minecraft, breaking the wall is an easier way to get the loot. The arrow trap can be disarmed by breaking the tripwire with shears.

Strongholds
Strongholds are large structures made of stone bricks. Due to containing the End portal, visiting one is required to beat the game. They can be found by using an eye of ender to make it fly towards one (although this may cause the eye of ender to break). Strongholds have several rooms inside, including staircases, libraries with loot chests, and the End portal room that also contains a silverfish spawner.

Shipwrecks
Shipwrecks are structures most commonly found underwater, consisting of a wooden ship with chests containing loot, usually including maps.

Ocean ruins
Structures containing magma blocks and a few loot chests.

Ocean monuments
Ocean monuments are structures found underwater made of prismarine and sea lanterns. They contain 3 Elder Guardians and blocks of gold. They are also the only place where guardians naturally spawn.

Igloos
Igloos are structures found in snowy biomes made of snow. All of them contain a bed, furnace, and crafting table, but some have a ladder leading to a basement under the carpet. This basement contains a chest that always has a golden apple (among other things), a brewing stand with a splash potion of weakness and a villager and a zombified villager that are both locked up. The splash potion of weakness and golden apple can be used to un-zombify the zombie villager.

Pillager outposts
Pillager outposts are large towers made of cobblestone and wood. They have a loot chest at the top and about 3 cages around them that can contain iron golems or rarely allays. They spawn pillagers around them, including raid captains, which can be used for starting raids.

NPC villages
Villages are groups of houses populated by villagers that can be traded with. See here for more detail.

Zombie variant
NPC villages may generate as zombie villages, with various blocks in the houses being replaced with cobwebs.

Nether fortresses
Large nether brick structures with blaze spawners and loot chests. See here for more detail.