Possible Clues:

• Director general rings peacekeeper for very long periods of time from underground lock-ups
• Waste long time in prisons
• One's upset by muck in underground rooms
• Where people once spent time underground
• Undiagnosed without aid from those underlying cells
• “Far over the misty mountains cold / To ____ deep, and caverns old” (The Hobbit)
• Where one might be shut up with 18 down for ages