Nightmare Dungeon Guide
Important: You can fast travel to Nightmare Dungeons by clicking on the Dungeon after activiating the sigil.
Sigil Crafting: When to do it? https://www.reddit.com/r/diablo4/comments/14ahzgh/nightmare_sigil_crafting_most_efficient_sigil/
Getting into Ancestral Tier Dungeons is the most important part of this.. otherwise, it's worth crafting sigils to get achievements -- particularly, 40, 50, 75, and 100.
You Should Target Level 31 Tiers for a Chance at Ultra Unique Gear.
https://www.youtube.com/watch?v=ul6a4pyM5U0 https://www.youtube.com/watch?v=gse_mPMOStw
https://docs.google.com/spreadsheets/d/1lJIPOom_2aRWkwzZHKGkkWU0mVCGV5kFZZXtgYuuYyo/htmlview#gid=2003750032