I’ve seen lots of suggestions for this but I thought I’d give my opinion.
The ladders in between rooms is a very clunky method of moving vertically; the ladders take up a whole middle part of the room.
My suggestions are this:
Stairs in the form of diagonal pipes or cells like tall rectangles that connect two rooms to one another (this could also add new fun window decorations)
Ladders against walls (so they aren’t awkwardly in the middle of the room)
Vertical pipes connecting between rooms or other pipes (similar to the first game)
Interior stairs between rooms (though this is probably tricky to achieve) this could also be paired with some method to make rooms above one another have a hole between them to make overhangs or balconies (also very diffiult but worth a shout)
Hear me out:
Alien force elevators like those in the Subnautica 1 Quarantine Enforcement Platform.

Wall ladders make so much sense, having them be awkwardly in the middle of things can be well awkward
Stairs would be nice.
Mini-elevators.
Wall-ladders would also be nice.
Also having the option to remove floor/roof between upper and lower compartments.

At minimum the size of the hole is way to small it needs to be big enough to just drop down without the pain

wall ladders seems like a no brainer so upvoted for that point alone, but I love the idea of removing floors and creating balconies too! lots of great ideas.