Molten Core may have once been a 40-man raid in WoW, but it can now be easily soloed or completed with a very small group depending on your level. If you're trying to complete the legendary Sulfuras, Hand of Ragnaros, this is an instance you'll want to farm every week! Getting attuned lets you get to MC quicker, here's how you can get attuned.
Start the Attunement Quest
Talk to the blood elf NPC that's on the way to Blackrock Depths. He'll give you the quest Attunement to the Core. After picking this quest up, it's time to head inside Blackrock Depths!
Finding the Core Fragment
Upon entering BRD, take the mole machine to past the Grim Guzzler. You will need to clear the upper city portion of the instance all the way past the Seven Dwarves room. After clearing this room, take a turn and follow the map towards the Molten Core entrance. Right outside the instance portal is the core fragment for the attunement quest.
Entering the Molten Core
After looting the core fragment, enter the MC instance portal, then exit to return the NPC. Once you hand in the attunement quest, the blood elf will be able to transport you directly to the Molten Core!