- "A giant energy crystal made using lost ancient technology. Cores this large are an extremely rare find. A researcher would probably know how to use this."
- — In-game description
The Giant Ancient Core is an item in The Legend of Zelda: Breath of the Wild. It is an extremely rare Guardian Part obtained by defeating certain types of Guardians or from Treasure Chests in certain Shrines and Lomei Labyrinth Island. Only three types of Guardians drop them: Guardian Stalkers, Guardian Skywatchers, and Guardian Turrets, though it is the rarest of all Guardian drops. Like all Guardian Parts, it is a piece of ancient machinery created by the ancient Sheikah. They can also be randomly acquired via the Amiibo Rune using the Breath of the Wild series Guardian Amiibo. Giant Ancient Cores are essentially bigger Ancient Cores both of which act as portable power sources for ancient technology such as Guardians though Giant Ancient Core can provide more energy than Ancient Cores due to their size.
Giant Ancient Cores can be used by Great Fairies to upgrade certain armor, mainly the Ancient Soldier Gear and the Divine Beast Helms. At the Akkala Ancient Tech Lab the Ancient Oven Cherry can use them to forge certain types of Ancient Soldier Gear after Link relights its Furnace during "Robbie's Research". They are only required for two pieces of equipment: the Ancient Bow and Shield which are two of the most useful Ancient Soldier Armaments for combating Guardians. Additionally like Monster Parts, Link can use them to create Elixirs by cooking them with Frogs, Lizards, or Bugs though this is generally considered a waste of such a rare material.