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.

Some structures resemble elements of the game. The city center bears a resemblance to early iterations of the warden's design, and other structures resemble pillager outposts and woodland mansion rooms.

Overall view
The following three renders are the same instance of ancient city.

Redstone circuits
Underneath the frame at the city center lies a series of hidden basements with naturally generating redstone circuitry.

The secret entrance is located at the base of the structure, underneath the wooden bridge between city center and the wall. There's a piston door which is controlled by a sculk sensor in the redstone circuits in the basement.

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

Center
2 (with some loots: chests/ancient_city) 3 28  10  1,140  7  45  6  2  6  205  95  2  1  2  2  7  (1 white candle in one block) 10 (2 white candles in one block) 5 (3 white candles in one block) 32 117  38  19  3  25  13  1  117  44  13  13  3  16  3  13  1  102  27  3  6  1  (with some loots: chests/ancient_city) 10 390  2  197  64  1  (with some loots: chests/ancient_city) 5 155  1  78  33  1  (with some loots: chests/ancient_city) 3 85  1  75  40  12  1  (with some loots: chests/ancient_city_ice_box) 10 384  21  2  2  228  150  8  9  1  3  1  2  62  4  1  8  30  3  3  16  135  64  20  84  35  3  4  87  2  20  4  10  1  19  29  3  (with some loots: chests/ancient_city) 46 157  23  73  1  1,038  3  69  17  (Waterlogged) 342 43  10  (1 white candle in one block) 14 (2 white candles in one block) 4 (3 white candles in one block) 3 (4 white candles in one block) 16 16  22  32  4  2  2  2  44  2  3  (1 white candle in one block) 1 (4 white candles in one block) 1 (with some loots: chests/ancient_city) 5 123  84  40  4  199  92  43  40  4  2  (with some loots: chests/ancient_city) 336 68  65  371  66  7  1  (with some loots: chests/ancient_city) 87 30  33  2  112  1  21  1  (with some loots: chests/ancient_city) 230 42  22  225  24
 * Ancient City barracks.png
 * Ancient City camp_1.png
 * Ancient City camp_2.png
 * Ancient City camp_3.png
 * Ancient City chamber_1.png
 * Ancient City chamber_2.png
 * Ancient City chamber_3.png
 * Ancient City ice_box_1.png
 * Ancient City large_pillar_1.png
 * Ancient City large_ruin_1.png
 * Ancient City medium_pillar_1.png
 * Ancient City medium_ruin_1.png
 * Ancient City medium_ruin_2.png
 * Ancient City sauna_1.png
 * Ancient City small_ruin_1.png
 * Ancient City small_ruin_2.png
 * Ancient City small_statue.png
 * Ancient City tall_ruin_1.png
 * Ancient City tall_ruin_2.png
 * Ancient City tall_ruin_3.png
 * Ancient City tall_ruin_4.png
 * }

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.