The "Great Underground Empire" is a fictional setting from the interactive fiction game series known as Zork. It is characterized by a vast network of tunnels, caverns, and ancient ruins, filled with treasures and dangers. Players explore this underground world, solving puzzles and encountering various creatures. The empire is known for its rich lore and history, including the rise and fall of its inhabitants, the Great Underground Empire itself. Players often seek to uncover the secrets of this realm while navigating its challenges, making it a classic example of early text-based adventure gaming.