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 勝者の弾. This guide covers the requirements, step-by-step access, important notes, and first-visit rewards for each one.

Oubliette

Located between 弾丸王の城塞 and メインガンジョン. Sewer-style layout full of garbage bags, toxic puddles, and harmless ブレット族 variants.

Cost: 2 keys (or 使い慣れたロックピック / ドリル as substitutes)

Steps to enter

1. 弾丸王の城塞 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); 使い慣れたロックピック or a ドリル 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 メガウォーターガン, 冷却剤
• 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 古びた紋章, required for the 正銃教団修道院
• First visit unlocks ダスター

正銃教団修道院

Located between メインガンジョン and ブラックパウダー採掘場. Gothic monastery aesthetic with stronger enemies than the surface floors.

Cost: must first complete the Oubliette and retrieve the 古びた紋章

Steps to enter

1. Pick up the 古びた紋章 from its fixed room inside the Oubliette — it occupies an armor slot and disappears the moment you take any damage
2. Carry the 古びた紋章 through the rest of the Oubliette and all of メインガンジョン without being hit
3. Find the altar room on メインガンジョン — 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 古びた紋章 on the altar to open a staircase leading into the 正銃教団修道院

Notes

• Any hit destroys the 古びた紋章 — if you're already low on health when entering the Oubliette, consider whether the escort is realistic
• Some rooms inside the 正銃教団修道院 contain permanently Jammed enemies regardless of your Curse level — they deal and take significantly more damage
• The 正銃教団修道院 always has a hidden room containing 真理の探求者 – ブラザー・アルバーン; opening his chest yields ウソの代償. This room spawns independently from normal secret room generation, so multiple secret rooms in one 正銃教団修道院 run are common

Rewards and unlocks

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

Resourceful Rat's Lair

Located between ブラックパウダー採掘場 and Hollow. Mine tunnel layout with no shops and no normal chest rooms. The most complex prerequisites — plan ahead across multiple runs.

Cost: かじられたカギ + 1 キー + 2 ブランクs (the キー can be swapped for 最期のカギ, KEY-47, or 使い慣れたロックピック; the かじられたカギ has no substitute)

Preparation

• Hard prerequisite: the かじられたカギ does not spawn in the shop at all until you have built the 過去を始末する弾. You have to finish the four-component run in Bullet That Can Kill the Past Guide before this route opens up
• The かじられたカギ first appears in a メインガンジョン shop for 1000 ケーシング; payment can be made in installments across runs, and once paid in full it costs 115 ケーシング on every later run. Discount items never lower its price
• The かじられたカギ can be stolen, but not with フックガン or the 十字キー 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 ムカつく手紙 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 ブラックパウダー採掘場, 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 ブランク anywhere in the room — short-range blank effects like ブランク弾 won't work, and the trapdoor never spawns in a shop room
3. Open the trapdoor with a キー 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 ブランク at the dead end to open the first hidden passage. If you have アーマー, deliberately falling into the nearby pit reveals this passage too, saving a ブランク
6. Walk to the next dead end and use a second ブランク to open the second hidden passage. This one counts as a separate room with no pit, so the second ブランク cannot be saved unless you have another way to hurt yourself
7. Open the final hatch with the かじられたカギ to enter the Lair

Notes

• 血染めのスカーフ lets you teleport past both hidden passages, skipping both ブランクs
• 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 ケーシング), 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 かしこいネズミ, the reward room has eight pedestals with ハートs, アーマー, キーs, ブランクs, ガラスガンストーン, and 弾薬
• Four special chests in the room require ネズミのカギs and contain エメンテーラー, 食べかけのチーズ, ネズミのお宝袋, and ラットブーツ. ネズミのカギs 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 ネズミのカギ is needed to feed it
• Feed the snake 4 guns or items and it follows you as a companion until the ドラガン fight, where it defects and is absorbed to trigger the Advanced Dragun. That is the route to 穴だらけの聖杯 and the "Advanced Slayer" achievement (the other is throwing a おかしなタマゴ into fire)
• The snake refuses こわれたテレビ, スポンジ, and 使い慣れたロックピック — do not count on those to make up the four
• Alternatively, you can kick the かしこいネズミ into the snake to feed it
• After the reward room you can proceed to the Hollow normally, or spend a ネズミのカギ to skip directly to the 鍛冶場
• First visit unlocks おかしなタマゴ

R&G Dept.

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

Cost: 1 勝者の弾 + 2 guns or items (sold to the 売り逃げ屋 in Hollow)

Steps to enter

1. Find the 売り逃げ屋 in Hollow
2. Sell the 勝者の弾 and 2 items — the entrance opens immediately after the third item is sold, so sell the 勝者の弾 last if you want to keep trading first

Notes

• The cost is steep: a 勝者の弾 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 アガンム there is no exit elevator — you have to throw yourself off the rooftop arena to reach the 鍛冶場
• 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