Dungeon of the Dead

The Dungeon of the Dead (死の迷宮) is a notorious dungeon located in the far North. It is the principal location of Goblin Slayer Side Story II: Dai Katana, and is also featured in Volume 8.

Overview
The Dungeon of the Dead is the deepest of all dungeons, consisting of ten levels. Ten years before the main plot, it served as the residence of the Demon Lord, during which it housed monsters of all kinds and spewed a plague of undeath and pestilence throughout the Four-Cornered World. A fortress city was then built in front of the dungeon to accommodate adventurers who wished to challenge it, though many died trying. Eventually, six adventurers would venture the dungeon and vanquish the Demon Lord, later becoming renown as the "All-Stars".

Since the Demon Lord's defeat, adventurers have dismissed the dungeon as something of the past, the monsters inhabiting having also since been cleared. However, the idea of challenging the Dungeon of the Dead remains a fearsome task, as shown during a meeting between Sword Maiden and the King's council.

Goblin Slayer Volume 8
A nobleman and a cultist of the God of Wisdom manipulated a horde of goblins to occupy the dungeon to summon a greater demon, and had them kidnap the Princess to be used as a sacrifice. Goblin Slayer's party ventured to the fourth level of the dungeon to rescue her, where they soon do battle with a greater demon's arm that burst from the goblin leader. When the adventurers are confronted by the surviving goblins attempting to leave, Sword Maiden bursts into the dungeon with a group of warrior-priests to kill the goblins.