Despite Diablo 4’s lengthy 35-hour campaign, it is only just the beginning of your journey through the death-riddled world of Sanctuary.
As with any self-respecting ARPG, farming loot is an essential part of increasing your power in order to take on the increasing challenges that lie ahead.
Nightmare Dungeons are one of the main components of Diablo 4’s endgame content and can grant you powerful and rare rewards.

What are Nightmare Dungeons in Diablo 4?
Nightmare Dungeons are punishingly difficult dungeons in Diablo 4 that offer powerful endgame gear and materials for completing them.
They will only appear once you have completed the campaign and the Cathedral of Light dungeon on World Tier 2.
This will open up the Nightmare difficulty, which allows Nightmare Sigils to emerge in Sanctuary. Nightmare Sigils are an essential requirement of Nightmare Dungeons and must be activated in order to get into them.
How to Get Nightmare Sigils in Diablo 4
Nightmare Sigils can be obtained from reward caches from the Tree of Whispers or as rare random drops from slain enemies and world bosses.
They will only start dropping once you’ve completed the Campaign and Cathedral of Light dungeon on World Tier 2.

Each Nightmare Sigil corresponds to a specific dungeon out in the world, each with its own modifiers that affect the rarity of the loot and the difficulty of the enemies. The dungeons will also have unique affixes that push you to change your playstyle to complete them.
The difficulty and level of rewards can be increased further if you decide to go into World Tier 4.
Each Nightmare Dungeon will have a difficulty tier of its own ranging from 1-100. World Tier 3 difficulty will have Nightmare Dungeons ranging from Tiers 1-20, while World Tier 4 will be from 21-100.

Nightmare Dungeon Rewards
If you manage to blast your way through these multi-tiered Nightmare Dungeons, a bunch of tantalizingly powerful endgame rewards will be waiting for you.
As well as getting a nice bump in loot quality, you’ll also get access to a variety of powerful Paragon Glyphs that can be used in conjunction with the Paragon Board – Diablo 4’s endgame skill tree.
When socketed, they will augment your Paragon abilities, increasing the power of surrounding abilities on the board and often granting highly unique and mighty bonuses.