Ancient City

An ancient city is a palatial structure found in deep dark biomes at layer -52, harboring chests containing items that cannot be found anywhere else or that help a player avoid a warden.

Environment aesthetics
An ancient city features a very large palace that stretches throughout a deep dark biome. The palace is made up of long corridors with some rugs made of blue, light blue and cyan wool or carpet floors to prevent vibrations as well as some smaller ruins off to the side of the main corridors, which contain between one or two loot chests. The city has statues and the center features a frame resembling a warden's head, where there are reinforced deepslate blocks, which is an unobtainable material in Survival mode. Other unique blocks such as soul lanterns and candles as well as different forms of deepslate and sculk can be found here.

File structure
All ancient city structures found below are located in the folder client.jar/data/minecraft/structures/ancient_city.

Redstone circuits
Underneath the frame at the city center lies a series of hidden rooms with naturally generating redstone circuitry, such as piston doors and logic gates. The secret entrance is located at the base of the structure, in front of the frame. There is a sculk sensor above it. Each variant of the city center uses a different redstone circuit to conceal the entrance. Sometimes there is nothing in front of the frame, while at other times, there can be a chest or a set of walls in front of the frame.

Loot
The loot in the chests includes several useful items for exploring the ancient city, such as snowballs and the Swift Sneak enchantment, as well as items that can't be found anywhere else, such as echo shards.

Trivia

 * Some statues scattered throughout the ancient cities, including the city center, bear a resemblance to early iterations of the warden's design.
 * There are structures that resemble pillager outposts and woodland mansion rooms.