The Last City is exactly what it seems like - the last city, holding out before the darkness.
Most people live in walled towns now, and perhaps in the old days, this “city” would have been considered merely a large town. But now it is filled to the brim. It is perhaps the definition of overcrowding. The large walls, the reason it held out in the first place, have become supports for multiple tiers of buldings, connected by raised walkways. The highest tier is covered with protective material of all kinds.
The city sat beside a river running out into the sea, but a part was diverted to quench a fire in the past, and nobody could restore this. Perhaps they didn’t want to, because at least it keeps the sewage out. Overcrowded, part-inundated, often dark, still, this is home to the largest collection of humans (in Middarmark?).
There is no one ruler, just factions yearning for power. If they could stand together, repair some of those old hulks in the bay, establish some contact… Only if.
(For me, this is like tiny Lankhmar meets Venice.)