The ancient city can be found in large caves, a "Warden" mob lives inside the city, which is very scary and dangerous, you need to keep away from it, since this mob makes a sound that darkens your eyes. The ancient city itself consists of these resources: Basalt, Deep Shale and Rock Blocks.
In the city you will find chests containing weapons and food for further survival in a dangerous place. You should also carefully inspect the territory, because you can get caught in traps from which it is difficult to get out.
Coordinates do not need to be entered, you will immediately find yourself in the biome.