Beneath the City are many tunnels and caverns and buried buildings and streets that have accumulated over the centuries that the City has been in existence. As new layers are added to the City, the old ones are buried and added to what is collectively termed the underground.
The upper levels contain buried streets that have been built over – lost cellars and ground floors with low ceilinged streets paved over to make room for new buildings as the people who live in the City change. Some of these streets have been converted into sewer systems and others still act as streets with people living away from what little sun there is.
The lower levels contain more purposeful tunnels, The beginnings of underground transport systems, old carriage routes, canals and subways. Many of them are collapsed or suffered damage from ancient earthquakes but there are still enough open that they can be used with relative safety if you know your way around.
The deepest levels of all contain natural rock fissures, underground portions of the river and cave systems. Even these caves are occupied by some people, however they are full of twists and turns and getting lost is incredibly easy. Many have gone down there and never returned, presumed lost forever in the maze. There are also many rumors of an enormous creature that stalks and hunts in the lower tunnels hunting and killing anyone who ventures down there unprepared, however no one alive can agree on what it looks like.
As with all places, the underground is full of those who have fallen through the cracks (metaphorical and literal) of surface society. Those who have no place or power in the world, those who even in this dimension find themselves hiding, those who have no place to go and are desperate to get out of the rain and those who need somewhere to stash the latest heist…
The dregs of society end up underground eking out an existence as best they can. As well as regular people living down here there are also smugglers and criminal gangs who either base themselves here out of the way of scrutiny or have safe houses and caches hidden underground for emergencies or merely use the underground as a way of traversing the city without being seen.
As well as the dispossessed you also find those who prefer living in the dark and many other strange creatures that have been summoned or altered by those above who have found themselves discarded down here and unexpectedly found themselves thriving.