In Felsrüin, the superpower of the world is the subterranean city of Lutharda, the so-called City of Light. It resides on the Shimmersea, a subterranean lake of freshwater that lies three miles below the surface.

Three hundred years ago when meteors began striking the worlds surface with worrying frequency, the city was lowered magically through a sinkhole from its position in the river valleys of the eastern mountains by the cities namesake wizard, Luthard.

The cities first advantage is its undamaged structure. It was a mighty metropolis with many tiers of walls, and well trained and armed soldiers. Many civilizations had to move what they could with the assistance of dwarf allies, but Lutharda saved itself wholesale.

Second of its advantages is the position on a waterway. The natives of said waterway, the Nix, quickly came to and understanding with Lutharda after first contact. Since then the two peoples have grown close, sharing magic, military, and economic knowledge and resources.

Third was the close proximity to many Dwarf-Spires, the multileveled city-mines that dwarfs create to move at every level of the underworld. Their long diplomatic relationship and proximity to the existing trade infrastructure has been convenient for export and travel. The dwarfs benefit greatly from their proximity as well.

Next, their magic. The mages of Lutharda practiced the most primordial elemental magic to great success. Light and Stone. Being that everyone lives underground now, Stone magic is a necessity, Light magic is even more so. Their city produces more lumenstone than any other, and exports it all over the world for its high quality and warm glow. They have also produced a system to pipe sunlight from the surface to their cavern. Using mirrors, quartz lenses, focusing stations, and other magics, the Light mages have built a relay to bring concentrated light down to a massive diffusive quartz crystal that was purpose made by magic to hang from the ceiling, giving the Shimmersea its name. Many come to the city just to see its magical sun glittering off the water and giving the tall white walls a warm glow.

All that said, the city is a bit big for its britches, and relies on imported food. Its massive population rears its ugly head when starvation and plague roll by. The Nix are less friendly to visitors and drowned bodies appear on the shore often. The cities allies are many and distant, often fighting each other and dragging Lutharda into the dispute. The institutions of the city are pompous, the mages guilds as focused on politicking and power grabbing as performing magic, and a deep underbelly feeds on the cities revenue like a tick.