Abandoned Mineshaft

Abandoned Mineshafts are generated structures in Minecraft added in the Adventure Update 1.8.

Specials
They hold specials like a Chest and a Cobweb. Inside the Chest there's Diamond, Golden Apple and Cocoa Beans. There's also cave spiders too and Rail.

Info Villager says
Sometimes mineshafts can be found floating in a Ravine.