The Chest of Akka is a chest that can be opened with a Key of Akka obtained from a Wormfeeder Rune. It and all other Wormfeeder Rune chests will reward engrams, Court of Oryx runes, Wormspore, and Calcified Fragment XXXVIII: The partition of death.
The chest is located in the Hall of Souls near the Court of Oryx.