Abandoned Mineshaft

Abandoned Mineshafts are naturally Generated Structures that form underground that were added in Update 0.9.0.

Structure
Abandoned Mineshafts are long winding maze-like structures. They usually begin with a large Dirt room, with an arched roof, and continue into a long tunnel-type maze, with Fences and Oak Planks approximately every 4 Blocks.

They will sometimes have Torches and Rails, along with large numbers of Cobwebs as well. Most Mineshafts also contain Cave Spider Spawners.

Mesa Mineshafts
Main Article: Mesa Mineshafts

Mesa Mineshafts are Abandoned Mineshafts that spawn in Mesa Biomes. They are made of Dark Oak Wood rather than Oak Wood and spawn on the surface. Gold Ore is found in plentiful quantities in these Mineshafts.

Trivia

 * Before Update 0.11.0, Mineshafts contained Spider Spawners.
 * Mineshafts can occasionally be intersected by a Stronghold or a Dungeon.
 * Some areas of the Mineshaft are lit by torches, but not enough to stop Mobs from spawning.
 * Sometimes, part of the Mineshaft can be missing or on Fire due to a natural Lava fall.
 * Mineshafts are not only very long, but can go from sea level to Bedrock.
 * Mineshafts are more likely to spawn the deeper underground the Player goes.
 * Before Update 0.14.0, Chests of loot could not be found in Mineshafts.
 * After Update 0.14.0, Mineshafts now have a chance to have a random Minecart with a chest containing loot.