Secret Floors Guide (Hidden Chambers)

Enter the Gungeon has a hidden chamber between each main floor (1.5 through 4.5). Defeating any secret floor boss flawlessly does not reward a Balle de conquête. This guide covers the requirements, step-by-step access, important notes, and first-visit rewards for each one.

Oubliette

Located between Forteresse du Seigneur du Plomb and Gungeon. Sewer-style layout full of garbage bags, toxic puddles, and harmless Balle variants.

Cost: 2 keys (or Matériel de crochetage / Perceuse as substitutes)

Steps to enter

1. Forteresse du Seigneur du Plomb always contains a fireplace room — find the blue water barrel inside or in an adjacent room
2. Push the barrel next to the fireplace to extinguish the flames
3. Crawl into the fireplace and interact with the hidden switch
4. A hidden room with a trapdoor appears on the map — the trapdoor has two locks, each costing 1 key (2 total); Matériel de crochetage or a Perceuse can substitute for normal keys

Notes

• Water barrels are fragile — enemy attacks and explosions destroy them, so position carefully during room clear
• If the barrel is gone, use Mégarroseur, Liquide refroidissement
• After your first visit, the water barrel usually spawns inside or directly adjacent to the fireplace room on all future runs

Rewards and unlocks

• A small fixed room inside the Oubliette always contains the Vieilles armoiries, required for the Abbaye de l'Arme Véritable
• First visit unlocks Tire-ordures

Abbaye de l'Arme Véritable

Located between Gungeon and Mine de Poudre à canon. Gothic monastery aesthetic with stronger enemies than the surface floors.

Cost: must first complete the Oubliette and retrieve the Vieilles armoiries

Steps to enter

1. Pick up the Vieilles armoiries from its fixed room inside the Oubliette — it occupies an armor slot and disappears the moment you take any damage
2. Carry the Vieilles armoiries through the rest of the Oubliette and all of Gungeon without being hit
3. Find the altar room on Gungeon — it contains seven large bullet warrior statues and looks one cell larger than a normal room on the map; it tends to appear near a shop or chest room
4. Place the Vieilles armoiries on the altar to open a staircase leading into the Abbaye de l'Arme Véritable

Notes

• Any hit destroys the Vieilles armoiries — if you're already low on health when entering the Oubliette, consider whether the escort is realistic
• Some rooms inside the Abbaye de l'Arme Véritable contain permanently Jammed enemies regardless of your Curse level — they deal and take significantly more damage
• The Abbaye de l'Arme Véritable always has a hidden room containing Chercheur de vérité – Brother Albern; opening his chest yields Mensonges. This room spawns independently from normal secret room generation, so multiple secret rooms in one Abbaye de l'Arme Véritable run are common

Rewards and unlocks

• Boss drops both a normal boss reward and a Synergy Chest
• Simply entering for the first time unlocks Broche sanglante and the "Reverence for the Dead" achievement — you do not need to clear the floor

Resourceful Rat's Lair

Located between Mine de Poudre à canon and Hollow. Mine tunnel layout with no shops and no normal chest rooms. The most complex prerequisites — plan ahead across multiple runs.

Cost: Clef rongée + 1 Clef + 2 Ballablancs (the Clef can be swapped for Clef cartouch'os, AKLÉ-47, or Matériel de crochetage; the Clef rongée has no substitute)

Preparation

• Hard prerequisite: the Clef rongée does not spawn in the shop at all until you have built the Balle Qui Peut Tuer le Passé. You have to finish the four-component run in Bullet That Can Kill the Past Guide before this route opens up
• The Clef rongée first appears in a Gungeon shop for 1000 Douilles; payment can be made in installments across runs, and once paid in full it costs 115 Douilles on every later run. Discount items never lower its price
• The Clef rongée can be stolen, but not with Grappin or the Pavé directionnel hook (see How to Steal from Shops); if stolen before it has been paid off once, it returns next run at the price it was at
• Six Message moqueur are scattered throughout all floors of Enter the Gungeon and appear randomly each run — pick them up whenever they show up. Each note ends with a cheese-wedge arrow indicating one direction in the maze; the more notes you have collected, the more of the correct sequence you know before entering the Lair

Steps to enter

1. On Mine de Poudre à canon, find a room with 2–4 rats running on the ground and clear it
2. Reveal the hidden trapdoor by walking repeatedly over suspicious floor tiles (a larger-than-normal dust cloud marks the right tile), spraying liquid on the ground, or using a Ballablanc anywhere in the room — short-range blank effects like Ballaballablanc won't work, and the trapdoor never spawns in a shop room
3. Open the trapdoor with a Clef and drop in
4. Walk along the minecart tracks to the end — do not ride the minecart (riding teleports you backwards repeatedly; walking is faster)
5. Use one Ballablanc at the dead end to open the first hidden passage. If you have Armure, deliberately falling into the nearby pit reveals this passage too, saving a Ballablanc
6. Walk to the next dead end and use a second Ballablanc to open the second hidden passage. This one counts as a separate room with no pit, so the second Ballablanc cannot be saved unless you have another way to hurt yourself
7. Open the final hatch with the Clef rongée to enter the Lair

Notes

• Étoffe sanglante lets you teleport past both hidden passages, skipping both Ballablancs
• The Lair shows only a rat-holding-cheese animation instead of a real map
• Candle-carrying rats wander the floors — harmless normally (they die on contact and sometimes drop Douilles), but become Jammed and deal contact damage if you carry any Curse
• The maze is a sequence of six rooms, each with a choice of exit direction. Wrong once: sent back to the previous room. Wrong twice: elevator to the Hollow, ending your Lair run
• The correct sequence is fixed per save file and stays the same forever once discovered

Rewards and unlocks

• After defeating the Le Rat Rusé, the reward room has eight pedestals with Cœurs, Armure, Clefs, Ballablancs, Pierre de Guon en verre, and Munitions
• Four special chests in the room require Clef du rats and contain Fromager, Fromage Grignoté, Sac Rusé, and Bottes de Rongeur. Clef du rats only drop during the third Punch-Out phase of the fight, up to six per fight
• The reward room also has a secret room with a snake hidden behind two locked doors — items can be dropped through the second door, so only one Clef du rat is needed to feed it
• Feed the snake 4 guns or items and it follows you as a companion until the Dragun fight, where it defects and is absorbed to trigger the Advanced Dragun. That is the route to Assassin Graal and the "Advanced Slayer" achievement (the other is throwing a Œuf Bizarroïde into fire)
• The snake refuses Télévision cassée, Éponge, and Matériel de crochetage — do not count on those to make up the four
• Alternatively, you can kick the Le Rat Rusé into the snake to feed it
• After the reward room you can proceed to the Hollow normally, or spend a Clef du rat to skip directly to the Forge
• First visit unlocks Œuf Bizarroïde

R&G Dept.

Located between Hollow and Forge. No connection to the other secret floors.

Cost: 1 Balle de conquête + 2 guns or items (sold to the Acheteur rampant in Hollow)

Steps to enter

1. Find the Acheteur rampant in Hollow
2. Sell the Balle de conquête and 2 items — the entrance opens immediately after the third item is sold, so sell the Balle de conquête last if you want to keep trading first

Notes

• The cost is steep: a Balle de conquête proves you cleared a boss without damage, and you lose two usable items on top of that
• R&G Dept. has no shop and sparse pickups
• The map outline is deliberately shaped like a handgun; after beating Agunim there is no exit elevator — you have to throw yourself off the rooftop arena to reach the Forge
• Only enter when your loadout has clear surplus — if your core weapon or survivability items are borderline, selling them for a bonus floor rarely pays off