Lothranis and Momagnon are where the highest level Resource digs for Blacksmith, Craftsman and Tailor are acquired, and also the highest level Herbs for the Apothecary craft. There are 20 or less spawns of each "mineral", and many spawns of Herbs.
Where previously in the cultivation saga (Level 89), Sages went to Brimstone Pit and Demons went to Eden to kill their enemies, now at level 100 cultivation, Sages are going to Lothranis and Demons going to Momagnon to contact and accept quests from their allies.
In the level 99 culti, there is no distinction between Sage and Demon; same quest.
The cultivation at level 89 is required to enter this dungeon. It is a source of ultimate materials for Frostcovered City orbs, for level 85 gear. This discrepancy has a tendency to direct players toward Twilight Temple level 80 and 90 gear instead