Through The Crowded Keep is an achievement unlocked upon completing all Area 2 levels on at least Insane difficulty, those being: Servants Quarters, Castle Armory, Hall of Court, and The Throne Room.
Related Achievements[]
The Body of The Beast - Completed all Area 2 levels on Hard
Through The Crowded Keep - Completed all Area 2 levels on Insane
Team Effort - Completed all levels with 4 active players on >= Medium Difficulty