The answer, from the developers
There is no method to open the third floor in the current build. The door is in the game. It stays locked. No quest, item or sequence opens it.
This is no longer second-hand. The developers published a public roadmap on Steam on 12 August 2026, and it says so directly:
"The Halloween Update will open the third floor of the Outpost and introduce a new questline, amongst other visual updates to celebrate the season."
So the correct answer to "how do I unlock the third floor" is: you don't, yet. It ships with the October update, along with new quests to do up there.
⚠️ Read the caveat the developers wrote themselves
The same post opens with this, and it is not boilerplate:
"Rather than a list of fixed dates, we'd like to share an overview of our goals for updates each month. We want to stay flexible enough to respond to your suggestions and feedback, so some details may update as development continues."
October is a stated goal, not a shipping date. It is signed by Miche & Nikko, who describe themselves in the same post as "a two-person team". Treat the month as intent.
It is the Outpost's third floor, not deep layer 3
Worth being precise about, because the two get mixed up constantly and the searches look identical.
- The third floor is a floor of your Outpost — the building with the shop, the workbench and the balconies. It is the locked door upstairs
- The deep layers are the dungeon you ride the elevator down into. Those go far past three and are open now
If you were looking for the dungeon, the descent is already available — see the elevator symbols for what each run throws at you.
What else is on the roadmap
| When | What the roadmap says |
|---|---|
| Within a month of 12 Aug | A batch of new constructs and a new vessel |
| September | The Deep Layers Update — one new biome and several new enemies |
| October | The Halloween Update — opens the Outpost's third floor, adds a new questline, seasonal visuals |
| Between updates | Fixes, performance, balancing, quality-of-life |
Also in progress at the time of writing: a public lobby browser — which shipped in patch 1.07 shortly after, covered on the how many players page.
What players report about the current state
From the Steam thread "This is the FULL game?":
- The third floor door is visibly present
- It remains locked
- One player: "I ran out of quests to do, yet the door to the 3rd floor is still locked"
- A third describes reaching a narrative dead-end — the story stops rather than concludes
That matches the roadmap exactly: the floor is built, gated, and waiting on the questline that comes with it. The story running out is the same gap, and it is the thing October is meant to fill. Where the current story stops is covered on the Ancient Secrets page.
The Biggy quest confusion
A Steam guide, Tips and tricks, says that completing Biggy's quests unlocks a new floor of the house, which has people grinding Biggie's quests expecting the third floor to open.
It is almost certainly not the third floor. The roadmap is unambiguous that the third floor arrives in October, and no player has reported opening it early. The other candidate is the second floor, which is gated behind a key — there is a Steam guide dedicated to reaching its balcony without that key — and which is where repairs and upgrades live.
We have not confirmed that Biggy's chain is what hands you the second-floor key, and the guide does not name the floor it means, so we are flagging the ambiguity rather than picking an answer. If you finished Biggy's chain and a third floor opened, that would contradict the developers' own post — and we would want to see it.
Why you are seeing "unlock guides" elsewhere
grain rot 3rd floor and how do i unlock the 3rd floor are searched often enough that
guide sites have pages for them. A locked door with no key is an awkward thing to publish,
and the incentive to invent a procedure is obvious.
If a guide gives you specific steps to unlock the third floor, check whether it names a source.
This page has an expiry date
The moment the October update lands, everything above becomes wrong. The Steam news feed is where it will be announced first — the same place the roadmap was posted.