Another dungeon located in Blackrock Mountains, Blackrock Caverns is a complex of tunnels created by Deathwing. It connects the mountain home of the Dark Iron dwarves with the Twilight Highlands, north-west of the Wetlands. It is populated by members of the Twilight Hammer and elementals. This is one of the first dungeons players can queue for in Cataclysm and chain-runs grant a ton of experience from 80-82. (Characters who complete the main dungeon quest series earn a fun deep-dive helmet for the duration of the instance.) Many players access the dungeon from This Can Only Mean One Thing..., taking Finkle's Mole Machine to the mountain.

Players who complete Dark Iron Contingency Plan with a Dwarf Rune Stone give their party Dark Iron Contingency Plan: Builders' emergency measures reduces elemental damage done to you by 5%.

From the Blizzard Community site:
"Rumors suggest that Deathwing himself carved out the subterranean labyrinth that allows the Twilight's Hammer to secretly transport elementals from the majestic Mount Hyjal to Blackrock Mountain. A vital hub of this shadow network is Blackrock Caverns, site of the cult's blistering forge and some of its most heinous experiments, including the transformation of cultists into twilight dragonkin.

In the bowels of Blackrock Mountain, beneath the more traversed parts of the mountain's spire, the Twilight's Hammer puts this hope into practice. Surrounded by boiling spouts of magma and burning rock - as well as the dangerous elementals that call Blackrock home - the cult will reforge their devoted in the image of the world they work to destroy."