Structure

This page lists generated structures in Minecraft. A generated structure is defined as any structure that is disabled when the "Generate structures" world creation option is turned off. Some structures, such as dungeons and desert wells, do still generate with this option turned off; however, they are listed on this page due to them having the appearance of an artificial structure as opposed to a natural formation.

Overworld
The Overworld contains numerous generated structures, at a wide variety of scales.

Underground structures
These structures can only generate underground in normal worlds, although in Superflat they can generate above ground $$ and in custom worlds mineshafts can generate aboveground in the void $$.

Aboveground structures
These structures only generate aboveground (the Igloo does have an underground portion sometimes)

Aboveground and Underground structures
These structures generate both aboveground and underground.

Underwater structures
Note that ocean ruins and shipwrecks sometimes generate above water on shores, and icebergs are partially above and below water.

The Nether
The Nether, though equally vast, contains far fewer generated structures than the Overworld.

The End
The End is the final and most barren dimension, with no generated structures on its main island. After defeating the ender dragon, gateways to the outer islands are created.

Structure-like Features
These worldgen features have similarities to structures but they are not true structures. Instead, they are coded and generated the same way as trees or ores. This is why they generate even when the "Generate structures" world option is disabled, and also cannot be located with the command.

Technical details
Structures are generated for a given chunk after the terrain has been formed. The chunk format includes a tag called that indicates whether structures whose point of origin is in that chunk have been generated. If it is false or missing, it generates again. Structure generation is based on what is already in the chunk, so (for example) flagging a chunk that has already been populated for repopulation approximately doubles the amount of ore in it. When structures are generated, they can spill over into neighboring chunks that have been previously generated.