Underfog

The Underfog, otherwise known as the Deep City, is an area beneath the city of Varawyn, populated by criminals and scientists with less than ethical intentions. Originally this area was the catacombs of an ancient city, but it now suits a much darker purpose.
The Underfog is an area of the city beyond the law. Local law enforcement consider the area mostly too dangerous to delve into. Other than the rampant crime, other dangers include strange monsters from the depths, and abominable creatures created by mad science.