Ancient Sewers

The Ancient Sewers is a third level biome.

One could believe that the sewers could not get worse than green. However, this deeper part of them is proof that it does get worse. Much, much, worse. An unusual filth gathers on the floor, the walls, the pipes, and the ceilings, hardening. The air is horrid, and would easily be a hazard for the lungs of many. Spiders have made their home among the crannies and cracks, and so has the slime mold. As well, all those undead bodies... All those rotting bones... They look appetizing for the hungry scavenging worms. And even the fungi has started to search for prey.

Access and exit
The Ancient Sewers can normally accessed from the Toxic Sewers after obtaining the Ram Rune, or from the Corrupted Prison after obtaining the Spider rune. When playing with 1 or more BSC active, a door in Prison Depths can also lead to this biome, though it requires the Spider Rune.

The only exit out of the Ancient Sewers leads to the Insufferable Crypt, where Conjunctivius awaits.

Scrolls
The Ancient Sewers contains 3 Power Scrolls and 2 Dual-stat scrolls, which cannot spawn in areas requiring the Teleport, Ram or Spider runes. On (2+ BSC) there is a bonus Power scroll. When 3 Boss Stem Cells are active, this biome has 3 guaranteed Scroll Fragments, and when 4/5 Boss Stem Cells are active, this biome has 5 guaranteed Scroll Fragments.

Enemy tier and gear level scaling
In the table below, you will find the gear level and enemy tier of the Ancient Sewers based on difficulty.

Boss Stem Cells rewards

 * 1 BSC: Treasure Chest
 * 2 BSC: Treasure Chest
 * 3 BSC: Treasure Chest
 * 4 BSC: Chained Items

Chests and loot

 * There is a 10% chance of finding a cursed chest in the level
 * Three treasure chest and a 2-choice item altar are found behind BSC doors

Shops
[needs confirmed data]

Secret areas

 * The blueprint for the Alchemic Carbine can be found in a secret area with poisonous water. The player must roll through a hidden path in the walls where the blueprint is located. This secret area will always be covered in poisonous water and there is no way of avoiding taking damage from it.
 * The blueprint for the Front Line Shield can be found in a puddle with poisonous water and that has a fake floor. The player must slam their way down to obtain it. Alternatively, the player can use the Homunculus Rune Icon.png Homunculus Rune to retrieve it, without taking damage from the poisonous water.
 * The blueprint for the Gold Preservation V upgrade can be found in a secret area concealed by cosmetic ground tiles with a maze that can only be navigated by the Homunculus Rune Icon.png Homunculus Rune. The player must first open the door with the rune's help, then progress downwards and solve another puzzle, before reaching the blueprint.

Enemy blueprints

 * The blueprint for the Sadist's Stiletto can be looted from Impalers.

Enemies
Many enemies are common between the Toxic and Ancient Sewers, including Disgusting Worms, Kamikazes, Scorpions and Zombies. A unique feature of the Ancient Sewers is the presence of the Impaler, which can sprout highly damaging spikes from the floor, remotely aiming for the player in a wide range, and usually does not spawn anywhere else. Apart from Zombies, which are replaced by Failed Experiments on 4+ BSC, all other enemies are present at all difficulty levels.

In the table below, you will find which enemies are present in the Ancient Sewers depending on difficulty level. For each enemy, any common, uncommon, rare or legendary blueprints they carry are indicated. When applicable, the minimum difficulty level for blueprint acquisition is specified in brackets.

Conjunctivius lore
Main Article: Conjunctivius

A series of lore rooms scattered around the Toxic Sewers and Ancient Sewers explain how Conjunctivius came to be.

It begins with a nameless, faceless corpse in the Sewers, likely infected by the Malaise. The body is bloated and one of its arms has mutated into a tentacle. Green goo trails from the body towards a small hole in the wall. After this encounter, the Beheaded finds that same trail of green goo and an empty cocoon next to a bigger hole in the wall, which was made by an adolescent Conjunctivius. Later, the player stumbles upon the trail of green goo close to a corpse. The trail leads to the remains of a huge cocoon and a gigantic hole, which was carved by the adult Conjunctivius as she escaped. Finally, a message left by soldiers tells how difficult it was to chain Conjunctivius, likely an order of the King. This explains why Conjunctivius is imprisoned in the Insufferable Crypt when the Beheaded arrives.

Malaise lore
Main article: Malaise The Sewers seem to have been central to the spread of the malaise, through the water supply system. For example, piles of contaminated bodies are found rotting in the sewer water. Upon finding them, the Beheaded wonders if those bodies are responsible for the initial infection of the citizens, or if those bodies only helped spread the Malaise by contaminating the whole water network. In a Grimoire found in the Sanctuary, the Alchemist writes that people believe the sap flowing through the walls of the Sanctuary is responsible for the Malaise, by contaminating the sewer network. He also suggests that this same substance could be the solution to the epidemic. it is unclear if the substance is in fact the source of the Malaise or if it's only a rumor. What is sure is that the Alchemist harvested and used this substance as part of a treatment for the infection, as indicated by the Grimoires of the Ossuary and the Clock Tower.

A giant broken door is found next to a soldier message warning not to open this door, lest the rats would get out and spread the Malaise. The Beheaded remarks that it is unlikely rats made such a big hole, which implies something else was kept behind the door. It is unclear who or what was behind the giant door. The lack of green goo trail, the fact that Conjunctivius is still in chains when the player reaches the Insufferable Crypt and this lore room being part of the "Infection" room series and not the "Beholder" (Conjunctivius's old name) series suggest that the creature which escaped was not Conjunctivius. The corpse of Prisoner 236 is found close by: he presumably died while trying to escape.

Alchemist Grimoires
Main Article: The Alchemist

In the Toxic and Ancient Sewers, the Alchemist was collecting mold and mushroom samples for his experiments. However, the growing numbers of revenants made his work increasingly difficult.


 * It is becoming increasingly difficult to collect mold samples in these sewers. There are too many revenants.

GIT GUD Room
Found in a secret entrance (may not spawn in every run), the room contains a corpse in the background, a campfire, and some wall scratchings that The Beheaded read as "GIT GUD". Upon interacting with the campfire, he will say "Something seems to be changing". Returning to the exit after interacting with the campfire will cause a zombie (or the Corpse Worm Variant of the Purulent Zombie) to spawn. When killed, this enemy will drop 50 cells.

Trivia

 * This biome is named "Old Sewers" in the past versions of the game.
 * The GIT GUD room is absurdly glitched. Players have reported that the spawn rate of the room is extremely low and the zombie has a low chance to drop 50 cells for unknown reasons.