The Stonecore is a dungeon located in Deepholm, introduced in World of Warcraft: Cataclysm. The entrance is at [47, 52] on the west side of the Temple of Earth, 2/3 to the top. Queuing for Stonecore through the Dungeon Finder requires an average item level of 272 and to discover the entrance.
Temple of Earth, Deepholm[47, 52]
High Priestess Azil
82 - 84
The Stonecore is located in Deepholm at the west side of of the Temple of Earth. The entrance is about two-thirds of the way up the central pillar. There's a distinct landing platform once you get to that level or higher.
The Stonecore is a 5-man dungeon designed for players leveling through Deepholm. It is located high in the Temple of Earth and requires a flying mount to reach. Once a sacred ground for the denizens of Deepholm, the Stonecore has almost completely fallen under the control of the Twilight Hammer. The High Priestess Azil herself is in charge here, but players may be more excited to see Millhouse Manastorm, who makes a brief appearance in the beginning of the dungeon.
This is a popular dungeon among players as the second boss, Slabhide, drops Reins of the Vitreous Stone Drake on both Normal and Heroic.
Players can complete Might of the Earthen with Dwarf Rune Stone for Might of the Earthen: Physical damage taken is reduced by 5% while you remain in the Stonecore.
From the Blizzard Community site:
"Within the Temple of Earth, locked in the heart of Deepholm, lies the Stonecore. It was inside these caverns that the Twilight's Hammer toiled over Deathwing, hammering elementium plates to the Dragon Aspect's body in an attempt to hold his tormented form together. With his renewal complete, Deathwing ascended into Azeroth, shattering the World Pillar and destabilizing the region of Deepholm.
These fanatics revere Deathwing as an agent of destruction, and his former lair as a sacred place. Yet, rather than accompany him into Azeroth, a massive number of cultists have gathered at the Stonecore. What they hope to call forth is yet unknown - but Deepholm, already shattered near to the point of collapse, cannot afford their success."