Since the growth of the City of Werms over the centuries of its founding, on the rocky pillars coming up out of the seemingly bottomless Cambio Delve, there has always been a demand for more space, closer and closer to the central portions of the city.
Because of this, layers of the city have become constructed over earlier layers of the city. Since much of the structure is out of the mined stone from the pillars the city is built on, the earlier layers are quite strong for the later layers to be built on, but of course styles change, and the uses and demands for buildings change, and the money and materials used to build the buildings all changes. So each new layer is different from the older layers, but the older layers are there. Deep, down below the current layers of the city. And things live there...
Of course, the poor of the city all live in deep levels of the city, where there are no living persons to remember who owns what patch of what stretch of stone building or plaza (long since blocked over by later construction, so hidden from fresh air and the sun). But the space is free. Also the lawless. The city of Werms is a pretty clean city, with a generally good alignment of the citizenry, but no city is free from corruption or crime. The lawless then drift to parts of the city where they can avoid the law. So gangs of thugs and criminals live in the lower levels of the city, far away from the sunlight, far away from the Baron's guard, and far away from the influence of the two Cathedrals and their clergy. Deep down, where the poor dwell - to fight with the other lawless, and to prey on the poor.
All this is to be expected in any city, where the older poorer parts of the city never get destroyed, but are used as layers of foundation for the later more prestigious layers of the city. But in Werms there is something more.
Deep, down in the lower levels, near to the base rock of the pillars and abutments coming up out of Cambio's Delve, there are holes. Rifts. Tunnels. All dug down into the rock of those pillars. In the early days of the city, they were known, and the things that crawled out of those holes were guarded against, and hunted and destroyed. But as layers of the city grew, the city servants and militia all worked the higher and higher layers of the city. Deep down, in the dark and forgotten depths - the ruins of the old city - the things that crawl out of the holes are still there. And they prey on the poor and lawless that are forced to live there.
One of the monstrosities that dwells under Werms is the horrid spider creature known as Ostigaar. Ostigaar is assumed to be related to some of the horrid creature hybrids that result from the strange religious and magical practices of the Dark Elves, but this is not confirmed. It has taken up residence in the bottom of what was once (in the early days of the city) a walled villa, but that and the surrounding layers were covered over after just a few hundred years, when the owning families fell into financial ruin, and there was requirement to reuse the real estate. Those layers above it were also subsequently covered over, in the fashion of how Werms has grown over the past millennium, and more.
In the buildings of the old villa, Ostigaar, and the horrid Unseely Realm creatures that serve her, are all still active, and prey on the foolish and foolhardy that dare to delve that deep into the city's past. However, there is a very good reason to delve down to the domain of Ostigaar, and brave the spider creature, and her servants - the villa that she dwells in is the (one time) famous home of the Harmalan family. This is the same family that produced the magical artifact, the Clockwork of Harmalan. Once the family was discredited, and the name bankrupted and forgotten, none cared about the Clockwork. But later generations (after the villa was sold, and covered over by later city growth) would remember the Clockwork, and the magic it is supposedly capable of, and begin to wonder. Could it be down there, among the fangs, webs, swords and spells?