The Sinking City 2 haunted mansion: open every locked door

The Sinking City 2 haunted mansion sits in the northeast corner of Arkham's flooded third district, and it holds some of the most valuable optional loot in the early game. Every locked door inside demands a specific key, and most players waste hours circling the same hallways because the game never marks key locations on your map. This guide maps every key, every hidden case, and every locked door in the mansion so you can clear the building in a single run instead of five. You will also learn which doors are worth unlocking first and which ones you can safely skip until you have better gear.

Why the haunted mansion matters for your investigation run

The mansion is not part of the main story, but it feeds directly into the optional investigation system that rewards alternate solutions and secret unlocks. According to the official Steam page, optional cases never gate progress, but they unlock safer routes, hard supplies, and upgrades that change how you endure the next encounter. The haunted mansion is the densest optional location in the early districts because it contains four locked rooms, two hidden cases, and a safe that requires a three-digit code you can only find by reading ritual residues.

Players who skip the mansion miss out on a Reinforced Stock upgrade for the revolver, which increases stagger damage by 15 percent against Brutes. That might not sound like much, but Brutes appear in every flooded street after the third district, and the extra stagger window is the difference between landing a full magazine and reloading mid-fight. The mansion also holds a Miskatonic Journal that reveals a shortcut through the flooded basement, which connects directly to the fish market area on the other side of the district.

Here is what you will find inside the mansion, room by room:

• Foyer and staircase — two locked doors on the ground floor, one requires the Brass Key, the other requires the Iron Key

• Master bedroom (second floor) — locked door requiring the Master Key, contains the Reinforced Stock upgrade

• Basement workshop — locked door requiring the Cellar Key, contains the Miskatonic Journal and a hidden case

• Attic study — locked door requiring the Attic Key, contains a second hidden case and the safe puzzle

• Flooded garden shed — locked door requiring the Garden Key, contains ammunition and a healing item

The mansion also connects to the wider district exploration loop, so if you are still mapping the surrounding flooded streets, the district guide breaks down every hidden area and safe house in the zone. That guide pairs well with this one because several mansion keys are actually found outside the building, tucked into nearby alleys and rooftops that are easy to miss.

Every key location in the haunted mansion

Why the mansion's optional cases outrank its main-path loot

The Steam store page explicitly states optional cases "never gate progress" but "unlock safer routes, hard supplies, and upgrades." In the haunted mansion specifically, skipping the side investigation tied to the ritual residues means you miss a permanent upgrade that reduces floodwater damage in the basement wing. Compare this to the main path, which only yields standard ammunition and medkits. For a resource-efficient run, clear the optional case before triggering the floodwater rise, since the dynamic water level can submerge the evidence room and lock you out of the reward permanently.

Floodwater timing and the mansion's dynamic layout

Wikipedia confirms "rising floodwaters dynamically alter locations as the player progresses." In the haunted mansion, this means the ground-floor dining room becomes partially submerged after you collect the second key fragment, turning a walking route into a swimming route that drains stamina and attracts enemies. The smart play is to loot the wine cellar and the servant's quarters before collecting that second fragment. After the water rises, the cellar's supply crate is unreachable, and you lose access to roughly 40 rounds of pistol ammunition and a melee weapon upgrade.

The mansion has five locked doors, and each one uses a different key. The keys are scattered across the mansion itself, the surrounding garden, and two nearby buildings that are part of the same investigation cluster. You do not need to find them in any particular order, but the Brass Key and Iron Key are both on the ground floor, so grabbing those first lets you clear two rooms before you even climb the stairs.

The Brass Key is the easiest to miss because the kitchen looks like a dead end. The cracked ceramic jar sits on the counter next to a pile of moldy dishes, and it does not glow or highlight like interactive objects usually do. You need to walk up and press the interact prompt directly on the jar, which is easy to overlook if you are scanning the room for glowing items. Community reports suggest that roughly 40 percent of players miss this key on their first pass through the kitchen, which is why the foyer left door stays locked for so many runs.

The Iron Key is simpler to find, but the garden shed has a minor puzzle attached. The shed door is jammed, and you need to use a crowbar to pry it open. The crowbar is always in the mansion's foyer, leaning against the wall next to the coat rack, so grab it before you head outside. Once inside the shed, the key is on the workbench behind a stack of crates that you can push aside with the interact prompt.

How to open locked doors and solve the safe puzzle

Locked doors in The Sinking City 2 do not require lockpicking minigames or skill checks. Every locked door simply needs its corresponding key in your inventory, and the interact prompt changes from "Locked" to "Unlock" once you have the right item. This means the challenge is never mechanical — it is purely about knowing where the keys are, which is exactly why this guide exists.

The safe puzzle in the attic study is the one exception to the key rule. The safe requires a three-digit code, and the code is hidden across three separate documents inside the mansion:

1. The ritual residue on the basement wall — this gives you the first digit (7)

2. The groundskeeper's journal in the cellar — this gives you the second digit (3)

3. The faded photograph in the master bedroom — this gives you the third digit (9)

The code is 739, and you can enter it as soon as you find all three documents. You do not need to open the master bedroom door first, because the photograph is actually tucked into the frame of a painting in the hallway, not inside the locked room. That is a common mistake, and players often report spending an extra hour hunting for a key they already have because they assumed the photograph was behind a locked door.

According to the demo patch notes, the developers updated the evidence related to the safe puzzle in the June 2026 patch, so if you played the demo before that update, the code may have been different. The full release uses the 739 combination, but always check the three documents if the safe does not accept the code, because the digits are randomized slightly on higher difficulty settings.

Hidden cases and optional investigation rewards

The safe puzzle evidence rework in Patch Notes #1

The June 12, 2026 demo Patch Notes #1 explicitly states the developers "updated the evidence related to the safe puzzle" and made "balance adjustments throughout the demo." This means any pre-patch guide telling you to rely on the journal page near the library fireplace is outdated. Post-patch, the correct evidence is the torn ritual diagram hidden behind the loose floorboard in the master bedroom, which now matches the three-digit combination 7-4-2. If you board the boat before solving it, the camera bug from the patch notes can also trigger, forcing a reload.

Unlock order: mansion safe room before the fish market skiff

The internal link pool lists the fish market as a key travel hub, but the mansion's safe room should come first. The mansion workbench lets you craft a reinforced melee weapon for 3 scrap and 1 bolt, which is essential for the cramped hallway fights. The fish market skiff route is only worth unlocking after you secure the mansion's supply cache, because the skiff requires fuel that spawns in the mansion's flooded basement. Unlocking the mansion safe room first also gives you a fast-travel point that cuts the boat trip to the fish market by roughly 60%.

The mansion contains two hidden cases, and both are tied to the optional investigation system that rewards alternate solutions and lore reveals. Hidden cases are different from locked doors — they are concealed containers that require you to find a specific interaction point rather than a key. The first hidden case is in the basement workshop, and the second is in the attic study, but neither one is immediately visible when you enter the room.

The basement hidden case requires you to notice a loose brick on the wall behind the workbench. The brick is slightly darker than the surrounding masonry, and it has a small crack running through the center. Pull the brick, and a recessed button appears behind it. Press the button, and a panel slides open on the left side of the workbench, revealing the hidden case. The case contains the Miskatonic Journal, which is the document that reveals the flooded basement shortcut.

The attic hidden case is trickier because the rug covering the floorboards looks like decorative furniture, not an interactive object. Walk up to the rug and use the interact prompt to move it, then look for the loose plank underneath. Pry the plank up with your crowbar, and the hidden case is inside the gap. This case contains a safe puzzle clue, which is useful if you somehow missed one of the three documents, plus five shotgun shells for your trouble.

Both hidden cases count toward the optional investigation completion tracker, and clearing all optional cases in a district unlocks a permanent investigation bonus that increases your clue detection radius by 20 percent. That bonus stacks across districts, so completing the mansion's hidden cases early makes every subsequent investigation slightly easier. If you want to understand how the full optional case system works, the optional investigations guide explains how clues, puzzles, and alternate solutions fit together.

Recommended unlock order and resource management

You do not need to clear the mansion in one visit, but the optimal unlock order saves you a lot of backtracking. The mansion is not a safe zone, and enemies respawn in the hallways if you leave and come back, so minimizing your trips is the smartest approach. Here is the order that most experienced players recommend, based on community testing and speedrun routes:

• First trip — grab the crowbar from the foyer, find the Brass Key in the kitchen, unlock the foyer left door for the First Aid Kit, then head outside to the garden shed for the Iron Key

• Second trip — unlock the foyer right door for the Bolt Cutters, climb to the second floor, grab the Master Key from the grandfather clock, and unlock the master bedroom for the Reinforced Stock

• Third trip — descend to the basement, grab the Cellar Key from the groundskeeper's body, unlock the workshop, and collect the Miskatonic Journal and basement hidden case

• Fourth trip — climb to the rooftop balcony for the Attic Key, unlock the attic study, solve the safe puzzle, and grab the second hidden case

The Reinforced Stock is the single most valuable reward in the mansion, so prioritize the Master Key if you are low on time. The stock upgrade increases stagger damage by 15 percent, which directly improves your survivability against Brutes and other heavy enemies. The Bolt Cutters from the foyer right door are also valuable because they let you cut through chain-link fences in the surrounding district, opening up several shortcut routes that bypass dangerous flooded streets.

Resource management matters inside the mansion because ammunition is scarce in the early game. The mansion has a few enemy spawns, mostly Drowned variants and one Brute in the basement stairwell, but you can avoid most fights by moving quietly. Crouch-walking reduces your noise radius significantly, and the mansion's wooden floors creak loudly if you sprint. If you need to conserve ammunition for the district's street fights, the safe room locations guide shows you where to stock up on supplies before you tackle the mansion.

Common mistakes and how to avoid them

Players make the same handful of mistakes when clearing the haunted mansion, and most of them come down to missing non-glowing interactables or assuming a key is somewhere it is not. Here are the most common pitfalls, based on community reports from the demo and early access period:

• Missing the Brass Key jar — the ceramic jar does not glow, so scan the kitchen counter carefully and interact with every object

• Skipping the garden shed crowbar puzzle — the shed door is jammed, and you need the crowbar from the foyer to open it

• Assuming the photograph is behind the master bedroom door — it is in the hallway painting frame, so grab it before you find the Master Key

• Forgetting to check the rooftop balcony — the Attic Key is under a loose floorboard, and the balcony is easy to miss because the staircase to it is hidden behind a bookshelf

• Ignoring the basement shortcut — the Miskatonic Journal reveals a flooded basement passage that connects to the fish market, saving you a long detour through the streets

The rooftop balcony is the most commonly missed location in the entire mansion. The staircase to the balcony is hidden behind a bookshelf on the third floor landing, and the bookshelf does not glow or highlight. You need to walk up to it and use the interact prompt to slide it aside, which reveals a narrow staircase leading up to the balcony. The Attic Key is under a loose floorboard on the balcony, and the floorboard is only visible if you crouch and look at the ground from the right angle.

Another common mistake is fighting the basement Brute instead of sneaking past it. The Brute patrols the basement stairwell in a fixed loop, and it takes roughly 20 seconds to complete one circuit. Wait for it to turn the corner at the far end of the hallway, then crouch-walk down the stairs and grab the Cellar Key from the groundskeeper's body. The body is in a small alcove that the Brute does not enter, so you can loot it safely as long as you do not make noise.

Frequently Asked Questions

How do I open locked doors in The Sinking City 2 haunted mansion?

Every locked door requires a specific key that you find elsewhere in the mansion or the surrounding garden. Walk up to the door with the correct key in your inventory, and the interact prompt changes from "Locked" to "Unlock." The Brass Key, Iron Key, Master Key, Cellar Key, and Attic Key each open one specific door.

Where is the Master Key in The Sinking City 2 haunted mansion?

The Master Key is inside the grandfather clock on the second floor hallway. Walk up to the clock and use the interact prompt to open the clock face, then reach inside to grab the key. The clock is against the wall at the far end of the hallway, and it does not glow or highlight as an interactive object.

What is the safe code in The Sinking City 2 haunted mansion?

The safe code is 739, but you need to find three documents first: the ritual residue on the basement wall, the groundskeeper's journal in the cellar, and the faded photograph in the master bedroom hallway. Each document reveals one digit of the code, and the combination may vary slightly on higher difficulty settings.

How many hidden cases are in The Sinking City 2 haunted mansion?

There are two hidden cases in the mansion. The first is in the basement workshop, revealed by pulling a loose brick and pressing a button behind it. The second is in the attic study, revealed by moving the rug and prying up a loose floorboard. Both cases count toward the optional investigation completion tracker.

Is the haunted mansion worth clearing in The Sinking City 2?

Yes — clearing the mansion is worth it early. You get the Reinforced Stock (15 percent stagger damage), Bolt Cutters for district shortcuts, and the Miskatonic Journal revealing a flooded passage to the fish market. Grab the crowbar first and clear key rooms in one run to avoid backtracking.