Gretretka

Maybe don't read this if you're not currently worldbuilding in the Underdark.

Gretretka is an ancient Underdark city populated by duergar, some second class non-duergar citizens, and slaves. Located where the Gretr Road meets the Impassable Sea and only two weeks' journey from the surface, it is a major trading hub for residents of the Underdark.

History
Gretretka is an ancient city, with all but its most recent history lost to the sands of time. The duergar may prize tradition, but this does not mean that they invest in history. Details are insignificant; the important thing is to preserve the spirit of the past. Most duergar know that the city - and possibly the entire cavern in which it and the Impassable Sea are housed - were created by Laduguer and given to the duergar as the place on which they work.

Geography
The duergar city is perfectly located for a major Underdark settlement. The Gretr Road meets the Impassable Sea at a river delta: numerous tributaries flow into the Sea in and around Gretretka, enabling both aquaculture and industry. The largest of the rivers, the Cramelia, travels alongside the Gretr Road in the sections closest to Gretretka; it bisects the city, dividing it into two primary sections and enabling fast waterborne travel from the northeast (by the Gretr Road) to the southwest (the delta). Between the rivers and tributaries are large expanses of water-smoothed stone leading down to the water's edge. The duergar have built their city up from these natural foundations, constructing tall (often adjoining the ceiling), functional buildings sensibly arranged.

The Cramelia River splits in two at the centre of Gretretka, dividing and around a massive column connecting the floor to the ceiling before rejoining into a single flow. This column is a duergar holy place: it houses the Church of Laduguer and the Agor.

The lands of the delta form a natural limit beyond which the duergar cannot expand, forcing them to build up (the aforementioned tall buildings) and in: the cave walls abutting the city have been continually excavated over millennia, giving them the consistency of swiss cheese. While there are two primary exits to the city - the main gate guarding the Gretr Road and the more open expanse of the delta - these cave wall excavations mean that there are in fact many ways for small groups of well-guided people to get in or out.

Demographics
Approximately 15,000 duergar dwell within the city's walls. Some roam outside for reasons of resource gathering or trade, but most return to their homes inside at the end of each "day." (The Church of Laduguer is responsible for maintaining the city's clock: it dims the bright lights of the central column to structure time.) The duergar are served by approximately 10,000 slaves of non-duergar. Approximately 1000 non-duergar residents - largely but not exclusively traders - make their homes in Gretretka as well.

Economy
Before the siege, Gretretka was a thriving, well-rounded city-state. Its economic power is derived in large part from the duergar's enslavement of other Underdark races. Slavery is indeed so significant to the economy that duergar coin represents portions of slaves, or, more precisely, portions of their hourly capacity to work.