Nightmare Dungeons are part of the Diablo 4 enf-game.
We’ve crafted a difficulty of Diablo dungeons straight out of your nightmares. No, really! Nightmare-difficulty dungeons in Diablo IV unlock upon locating your first Nightmare Sigil. Each sigil corresponds to a specific dungeon somewhere within Sanctuary. These sigils will add special modifiers to their dungeon, increasing the ferocity of the hell-servants waiting for you inside and providing higher-rarity loot. Through completing Nightmare dungeons, you will recover even more powerful sigils, introducing increasingly death-defying modifications and challenges for you to overcome. As you progress into higher and more challenging World Tiers, new Nightmare Dungeons will become available for you to explore.