The Underground is what people don't see about the city. It might be literally underground, like sewers or burial chambers, or just necessary but boring infrastructure like aqueducts.

• What vital services does the Underground provide?
• How does the Underground physically connect with the rest of the city?
• Who lives here, and what do they do?

The Underground is what people don't want to see about the city. It is the filthy waterways and skull-strewn tombs. It has been abandoned or is being misused, and may be dangerous due to its inhabitants or simple neglect.

• How much of the Underground still functions? What has broken down?
• What social ills, like disease or poverty, have taken hold?
• Who lives here, and how are they suffering?