GRAIN ROT floor 2 not opening — what to do

First, work out which floor you are actually stuck on, because the two problems have completely different answers.

If floor 2 will not open

Community It is quest progression, not an item hunt. The answer players give each other in the Steam discussions is blunt: “By doing the quests, doesn’t take long.” There is no second-floor key to go and find in the Deep Layers before the quest line asks for one.

If the objectives have dried up before the floor opened, the thing to check is room levels. One player’s summary: “Certain Progressions are locked behind room lvls to get better items.” Spend a haul on upgrades and see whether a new objective appears.

“It was open, then my friend joined and it wasn’t”

Work out who is hosting first, because the two cases are different.

Community If you joined them, you are playing their save. Host-owned progression is the standard arrangement for this kind of co-op and it matches what players describe, but the developers have not documented it and we have not found a thread stating it outright — so treat it as the likely explanation rather than a confirmed rule. On that reading, their Outpost state is the one you see, your own unlocks are not carried across, and a host who is further behind you shows you a locked floor. Decide whose save you are pushing forward and play in that one.

If you are still the host and the floor closed when someone joined, that is not explained by save ownership, and we are not going to pretend it is. Nothing official describes such a behaviour and we have not found a player report confirming it either. Check the obvious first — that you are loading the same save, and that the objective you completed is still marked complete — and if it holds up, treat it as a bug worth reporting. The developers have shipped fixes for exactly this shape of problem: patch 1.03 fixed a bunker door in the ancient facilities that “could not be opened by clients”, and patch 1.04 fixed players being unable to respawn “because the area was blocked”. They are responsive, and a clear report is useful to them.

Then you still have to burn it

Opening the floor is not the same as being able to use it. The second floor is covered in Grain Rot, and that has to be cleared with fire before the space is any use.

The growth is a real object rather than decoration — patch 1.04 includes “Fixed a bug where Grain Rot was visible through certain unrepaired ceiling modules”, which tells you the game tracks it per module.

Community Three fire sources come up repeatedly in the discussions:

• The flamethrower bot from the Deep Layers. One player’s instruction: “find the firefly bot (the one that acts as a flamethrower) and posses it. You now have the means to remove the grain rot.” Another simply reported “FireBot was easy to use.” Players have not settled on one name for it, and the developers have not published one, so treat both as nicknames.
• Lanterns. “just craft lanterns and smash them or grab the desk lantern.” With a warning attached: “if you break it before turning it off it might spill flames everywhere.” Turn it off, then break it.
• A flamethrower from the shop, described as a shop-level unlock. Nobody in that thread pinned down which level, so we are not going to invent a number.

Getting the fire up there

Load it into the elevator. As one player put it, “anything loaded on the elevator comes home with you, even loose gear, furniture, constructs” — which is the reliable way to bring a fire source home rather than hoping to find one upstairs.

Fire hurts you too

Patch 1.04 records a fix so that “Vessels can now be on all balconies without taking any fire damage” — which is a plain statement that fire damages vessels elsewhere. Burn the growth, then get out of it. Do not park your vessel in the flames while you tidy up.

If it is floor 3 that will not open

That one is not your fault and there is nothing to solve.

Community A player asking where to find the third-floor key was answered: “its not in the game yet got the anwser from the dev on discord.” Multiple players in the same thread reported running out of quests entirely and finding the door still shut.

So the locked door upstairs is a scheduled feature, not a bug and not a hidden puzzle. If you have cleared everything else, you have reached the current end of the game rather than missed something. The full roadmap has what arrives before then.