I think there's two right now: a cave close to ragni's north exit, and downstairs a structure between nivla woods and time valley. Like xp grind spots, lots of mobs spawn there, but instead they give 0xp and have lots of loot drops.
More of a question than a suggestion but would it be healthy for the game to have more of those in higher levels? They can be an alternative to lootrunning and forgery for mythic hunting, and loot parties can develop from these (like xp parties, but for loot). Idk how those would look like (probably a mess) but it's interesting to think about.

