Minecraft wiki entry for Development_versions, associated text: Generates within the deep dark biome and includes all of the deep dark features within it.
Always generated at Y=-52.
Made of deepslate and its variants, basalt and its variants, and gray wool.
Contains soul sand, soul fire and soul lanterns, as well as candles and skeleton skulls.
Contains chests with unique loot, like the swift sneak enchantment.
Other valuable loot includes the "otherside" music disc, Potions of Regeneration II, enchanted books, enchanted iron and diamond leggings, enchanted diamond hoes, and enchanted golden apples.
If the frame of reinforced deepslate generates with a chest in front, it will always contain one golden carrot (a hint about how to open the secret door below).
Has different levels and open spaces, with several types of ruins and wall structures.
Some of these structures contain dark oak logs, planks, and fences; cyan, light blue, and blue wool and carpets; ladders; ice and its variants; note blocks; stone pressure plates; and iron trapdoors opened with levers.
Hidden underneath the frame of reinforced deepslate are several rooms containing redstone mechanisms that serve to introduce new players to their function.
There is a silenced sculk sensor that needs a signal strength of 8 to open a redstone door. Taking the golden carrot from the chest placed near the structure and eating it will reveal the entrance.
Each variant of the city center has a different redstone puzzle concealing the entrance, requiring slightly different strategies to solve.
The mechanisms are made with redstone dust, redstone torches, redstone repeaters, redstone comparators, redstone lamps, blocks of redstone, sticky pistons, a sculk sensor, a target, and a lectern.
One variant includes a lever, and another includes a furnace containing 24 deepslate and a wooden shovel.